Mac Pro suffering from kernel panics almost daily

Question

After running flawlessly for 2 years, my 6 Gig Mac Pro has started to suffer a kernel panic about once a day. Nothing really has changed as far as I know. Two details, probably irrelevant, I installed Lion about a month+ ago. And I have had an Android tablet attached via USB and enabled for remote debugging.

I ran a memory diagnostic (rember) and it didn't find any problems.

This is what I find in the Kernel log just before the crash:

Sep 22 15:27:59 monster kernel[0]: (default pager): [KERNEL]: ps_select_segment - send HI_WAT_ALERT
Sep 22 15:28:00 monster kernel[0]: macx_swapon SUCCESS
Sep 22 15:28:32 monster kernel[0]: (default pager): [KERNEL]: ps_select_segment - send HI_WAT_ALERT
Sep 22 15:28:34 monster kernel[0]: macx_swapon SUCCESS

I've seen a variety of messages mentioning these errors but nothing conclusive.

If there's a hardware problem, is there a definitive diagnostic that I can run to prove or disprove it?

Any tips or troubleshooting guide will be appreciated! Thanks,

Pito