I've been using an old Nokia branded 4GB micro SD card for the last few days since my Pi arrived - it's been fine.
My new super-duper 8GB Sandisk Ultra (Class 6/30 mb/s - deliberately avoided Class 10) micro SD cards arrived today from Amazon and immediately produced a "timeout waiting for hardware interrupt" when trying to boot the same Debian Squeeze image the Nokia card was using. So in spite of thinking I'd ordered suitable cards, I plainly hadn't...
So I tried Wheezy. Worked straight away! So it's a software thing and not the Pi hardware?!. Anyone know if there's any chance of getting a later version of the Squeeze image posted that has whatever the fixes are within it? I'm sure it would make more SD cards "compatible" and make life easier for other noobies like me...