[SGVHAK] Pi stability issues

[Braddock Gaskill]

My Raspberry Pi is breaking my heart.  I've got it all set to go online as
a dial-in non-BBS, but I can't get more than three hours of uptime before
it crashes.  No warning, no errors, no syslog output - it just freezes.

The Pi is notoriously finicky about power.  So I've tried powering it with
the 700mA micro-USB power adaptor that RS sold to me with it, two different
hubs, one of which was rated for 3.5 Amps, and the other actually listed on
the Raspberry Pi verified hub list.  I've measured the bus voltage at
between 4.8 and 5.2 volts depending on how I'm powering it, but even in a
setup with a nice 5.05V reading it still crashes.  I've even tried powering
it from one hub while using a second powered hub for the peripherals.

The Pi is hooked up to a powered USB hub, which is connected to an RS-232
converter and a USB modem.  The Pi is connected to ethernet and a 32GB SD
Card (and I've tried a different card but it was still unstable).  I've
reinstalled from scratch four or five times now.  Everything seems to
function normally until it doesn't.  I've tried it both in and out of the
enclosure I bought with it.  Running Raspian wheazy distro, with all
updates installed.

I've run memtester and iozone for long periods to stress it out without
errors or a crash, but a couple hours of completely idle time later its
dead again.

Argh.

Any ideas?  Are Pis normally stable?

-braddock