I spent most of the week dealing with the problems on my home machine of a zealous upgrading of GCC followed by recompiling various bits of infrastructure with high optimization. The slight hitch was that everything it touched turned to SIGSEGV. After several abortive attempts to get the new GCC to work, I fell back to the previous version, and miraculously everything worked again.
Then earlier today, I "upgraded" the BIOS on the computer. Suddenly both Windows and FreeBSD were panicking while loading their respective kernels. Um... problem. Fortunately the demons of "I told you so" failed to reckon with my l33t underclocking skills. After noticing that it got a bit further after leaving the machine off for I while, I tried dropping the clock speed. That seemed to leave the system stable enough to get to a point where I could roll-back the BIOS to the previous version, and miraculously everything worked again.