Interesting. None of my machines has ever had a huge problem with clock drift, except now and then the VMware-Server-based Ubuntu (6.x or 7.x [kernel 2.6.17-12 I think]) on my main desktop, and then it's usually temporary. A new WU or restarting the client OS has cured it, and it's been rare enough for me that I never cared to get to the bottom of it, especially when my main problem had been process priority for Linux SMP client vs. the GPU client.
Having written that, reading the man page for hwclock certainly goes into the mess that is involved in synchronizing clocks and the consequences. It's good that someone came up with a clever way to make it easy to auto-adjust for reasonable drift values, at least. Having to do it every several minutes would be rather unfortunate. I'd estimate that an adjust every 10 or 15 minutes would be more than enough, even though it might cause problems for monitoring software accuracy.
And that reminds me... I keep forgetting my C2D lost one of its sticks of RAM due to the continuing problem of Crucial Ballistix DDR2 failing on me. I
think the stick that failed was actually one of the replacement pair I got from Crucial for an earlier failed pair. The other is now all that's left between that machine and me having to, *gulp*, spend money on it. Except it's elderly and I don't wish to spend on it any more. I should probably sell it (the C2D 6400, the Gigabyte 965P mobo it's running on, and the RAM, after getting another free replacement from Crucial for the next owner to concern himself with), get rid of another low-performance SMP folder (X2-3800), and replace them with an 8 core machine ready to try -bigadv WU's. But the -passkey requirement irks me, and I'm going to have to do power calculations which will be difficult to find accurate figures for in order to compute them. At least I'll get an estimate of whether it's worth the effort and what the electrical costs or savings would be (because I might retire other power-hungry producers too, depending on output).
I'm also reminded now would probably be a good time to start up my months-old "new" Ubuntu 9.x install and make sure it's got all its updates. Eventually it will get my current SMP client, if I quit reading about performance and other problems for a long enough time.
Sorry for the wordiness, but I'm a bit more relaxed than usual thanks to consuming a bit more alcohol than usual for a weeknight.