Also gets rid of the Radeon's 5 year warranty I have not overclocked one, but the Radeon 64MB that I installed in a customer's system ran cooler than any other video card I have fooled with. I was actually able to place my finger on the rear of the core and keep it there. It was just warm. From what I understand, they really do not need the HSF at default settings. It was put there more for cosmetic reasons than anything else. Also from reading the posts at a Radeon support BBS and reviews, there is not much of a performance benefit when they are overclocked, at least where the 64MB version is concerned.
Have you ran benchmarks at default core/memory compared to it being overclocked? I am curious what your results were.
EDIT: Don't get me wrong about the warranty thing. I have cracked open my fair share of "classic" Athlons knowing that I would more than likely upgrade well before the warranty was up, but in the Radeon's case, I think that it will become a "keeper" in many people's systems for long enough that a 5 year warranty is worth considering not voiding. Even though the HSF may not really be "needed", it would be grounds to deny warranty service if found to have been tampered with. I am sure that ATI would be able to tell that the HSF was taken off, even if the stock one was put back on if sent back for a warranty RMA. I have heard of other card manufacture's denying warranty claims for the same reason