A bunch of people found this weblog looking for Ubuntu hangs in PCMCIA CS (Card Services) whilst upgrading from 5.10 to 6.06. In case it's not clear from my previous post, the problem appears to be related to using a 686-smp (and probably k7-smp) kernel on certain classes of hardware. I've seen it myself on the Asus P5LD2 motherboard (mine's a rev 1.02 VM model). Symptoms are hangs on dist-upgrades or upgrades done using the update manager. It seems to trigger a CPU-intensive loop of some sort on PCMCIA, and for me, it hangs altogether starting ACPI services. (Why PCMCIA is appropriate on desktop class hardware, I've no idea. Perhaps somebody can illuminate me.) This bug is reported in Ubuntu's launchpad as bug 37430.
To my knowledge, despite the "Fix Released" moniker, this still occurs - I tried it yesterday, post-release.
The workaround is to boot a -386 kernel first. The fix, if your pooch has already been screwed by this, is described in the bug report. You'll need a boot / rescue CD and a little knowledge of dpkg.