Installation
From here on in anybody reading this review should have less trouble than myself while installing a SLK-800U.

Removal of the motherboard from its case in this situation is unfortunately mandatory. Place the clear plastic sheet on top of the x-shaped motherboard mounting panel and place the motherboard on top of this. I took no chances and placed four washers directly between the mounting panel and the motherboard. There is a high chance that without these washers the motherboard would be short circuited by the panel, which to those who haven't already realized, is bad news.

Line up mounting holes with mounting holes, and grab a fake standoff. These special standoffs have extra-long male ends, the upper half without threads. Insert the male end through another clear motherboard washer, and place this end through the motherboard mounting holes into the mounting panel. Turn counter-clockwise until a small amount of slack is still present but stop before any one becomes too tight. Turn the motherboard on its edge and make sure no corners are too close to the motherboard and that some are not: excessive pressure from the panel on the mainboard is not a good thing. The next logical step would be to remove the base cover, apply your favourite thermal compound to both the CPU and heatsink, and plop it on top. This is NOT the next step in the installation phase. Thermalright's heatsink is too narrow to rely on the supplied heatsink cushions provided on AMD's CPU cores, so one should apply the 3M pads to the four dimples on the heatsink. Now you may return to thermal pasting and lining up the heatsink with the fake standoffs. Now place the metal washers on top of the black piece of metal encircling the SLK-800U, overtop the holes lining up with the standoffs. Install spring screws into standoffs, and your heatsink is installed. Now, choose your fan, place fan mounting clips into the appropriate holes with the clip facing towards the inside of the fan, place fan on heatsink, and pull the clips overtop into the mounting holes. You're set!

Test Rig
After all this hard work, we get to have a little fun.
Here's the related machine specs on which the SLK-800U was tested with:

AMD AthlonXP 2100+ Palomino
Abit KX7-333 (note: the KX7-333 is equipped with a CPU thermal diode longer than usual, which touches the underside of the processor and detects hotter than average temperatures, yet are still lower than the actual die temperature readings)
Thermaltake Xaser II A5000B case
ToCools Novasonic
80x25mm Delta fan which was used on both heatsinks, pushing 44cfm at 40dB/a
Nanotherm Silver thermal compound

Results
Ambient temperatures were measured by Thermaltake's Hardcano 7 Temperature sensor. CPU load temperatures were achieved with the assistance of Folding@home, and then in case that wasn't enough already, by running HotCPU Testor for 10 minutes. Temperatures were stable in all areas.

Conclusion

The 3DVelocity 'Dual Conclusions Concept' Explained: After discussing this concept with users as well as companies and vendors we work with, 3DVelocity have decided that where necessary we shall aim to introduce our 'Dual Conclusions Concept' to sum up our thoughts and impressions on the hardware we review. As the needs of the more experienced users and enthusiasts have increased, it has become more difficult to factor in all the aspects that such a user would find important, while also being fair to products that may lack these high end "bonus" capabilities but which still represent a very good buy for the more traditional and more prevalent mainstream user. The two catergories we've used are:

The Mainstream User ~ The mainstream user is likely to put price, stock performance, value for money, reliability and/or warranty terms ahead of the need for hardware that operates beyond its design specifications. The mainstream user may be a PC novice or may be an experienced user, however their needs are clearly very different to those of the enthusiast, in that they want to buy products that operate efficiently and reliably within their advertised parameters.

The Enthusiast ~ The enthusiast cares about all the things that the mainstream user cares about but is more likely to accept a weakness in one or more of these things in exchange for some measure of performance or functionality beyond its design brief. For example, a high priced motherboard may be tolerated in exchange for unusually high levels of overclocking ability or alternatively an unusually large heat sink with a very poor fixing mechanism may be considered acceptable if it offers significantly superior cooling in return.

Mainstream User:

While $43 isn't a lot of money, there are always cheaper alternatives such as CoughStockCoughHeatsinksCough which would yield the same important results: the computer turns on! While a very small percentage of computers are ever overclocked and heat is not usually an issue on out-of-the-box PCs I would have to say this heatsink is overkill. Considering installation requires the removal of the motherboard which is a bit of a PITA try and remember how most mainstream users do not know how to install a motherboard properly. On the bright side, it is very securely fastened after installation and probably poses less of a threat to your hardware than a stock heatsink clamping onto those socket lugs. Lacking a fan and instructions makes this just slightly less appealing to someone who either doesn't know what they're doing, or simply can't be bothered to buy a proper fan.

Enthusiast:

As far as cooling capacity goes, this heatsink sure pulls its weight. It beat out my previous heatsink, the ToCools Novasonic, by three degrees Celsius with a handicap of 1C ambient. While we're still over 40C, remember the ABIT thermal sensor actually touches the CPU and this happens to be a stock palomino so those ratings are nothing to scoff at! Apart from being an incomplete CPU cooler, requiring difficult installation procedures (we sure took care of that!) and lacking instructions, I have found nothing to complain about regarding this heatsink. Its design is tight and strong. It performs well above the competition. It includes mounting hardware for many sizes of fans. It fits both AMD and Intel CPUs. It is very securely mounted on the motherboard and poses a minimal threat to going the way of standard CPU lug-mounted heatsinks imitating a brick in the event of a dropped case. At $43 you're getting a great deal as you probably get better performance out of this than your average $120 watercooling setup! If you're serious about cooling air-cooling does you fine the SLK-800-U is your best buy.

Be sure to pick up a Thermalright SLK-800-U from Newegg at $42.99!