OpenSUSE :: Segfaults On Cold Boot But Not "warm" Boot?

Generally, my computer behaves okay. Sometimes, however, it crashes and is unstable until after I shut it down, wait ten seconds and boot it up again (what I'd possibly incorrectly call a warm boot). It only ever seems to need a "warm boot" after being off for over a day (e.g. when the in-laws visit for an evening and I don't use my computer from Wednesday night until Friday night). I've been poking and prodding the problem as best I know, but I've not worked out what the problem is. The kernel is still awake enough to respond to SysReq and so I can reboot cleanly if my machine locks up, but it was only in the past couple of days that I noticed segfault messages.

Sometimes Chromium will crash out and refuse to restart after that because of segfaults. Sometimes X locks up and I can't switch to another terminal. Sometimes X just restarts itself (normally alternating between Ctrl+Alt+F7 and F8), but once that happens then X won't stay stable. I've also once seen some "preload" command segfault on TTY1 (not sure which one it was). I've run memtest a couple of times and it passes a couple of iterations each time before I finish it. I've moved my memory around in case it isn't seating properly. I've tried hammering the processor with some of the performance testing in Parted Magic. I've swapped out the graphics card (partly to see if it was sending bad messages, because I've had other problems - reported in other threads) with no effect. The BIOS is still keeping the time, so it wouldn't seem to be anything battery related (plus the mobo is only about a year old).

I can't work out what causes it, but if I power off, wait and power on again then everything is fine. The only stack traces I've seen have been "segfault at 8 ip ..... error 4 in libstdc++.so.6.0.14" and "/usr/bin/Xorg - corrupted doubly linked list". Google wasn't much help, because so many segfault questions are people working with their own apps that they're writing (where it is their mistake) or some desktop app (where it is still the same type of mistake, but it can be run through GBD, unlike the entire OS). I'm running openSUSE 11.4 with all the latest updates, plus Gnome 3.