Posting my personal experiences in the hope it helps someone else.
I ordered my Pi from RS, and choose the additional Transcend 4GB SD card to save me having to figure out which compatible card to buy.
It took me hours to get that card to boot, after formatting, reformatting, checking for bad sectors, using both the arm installer and the win32 disk imager. Even with no USB or network cable plugged in I got errors.
It would hanging at various parts of the startup that seemed to indiicate insufficent power, even though I had a choice of two recommended PSUs (Kindle and HTC).
Eventually it settled down and was more consistent, I could always get to the command prompt on login, but when I ran startx the mouse and keyboard froze (could still SSH in though).
Didn't seem to be a mouse/keyboard issue as they worked fine in OpenElec.
Today I installed Debian on Sandisk Ultra 4GB class 4, and everything works perfectly. Boots every time, keyboard and mouse work in the GUI.
I'd say it's worth having a few SD cards to hand, and take the 'supported' card list with a pinch of salt. I would have saved myself many hours of trouble if I'd started with a good card. Disappointing that it was one that was supposed to work according to the supplier, but never mind.
FYI the working parts I have are:
PSU: Kindle, HTC and Garmin Watch
Keyboard: a rubber flexible one I got off eBay
Mouse: logitech M-UAE96
SD: Sandisk Ultra HC 15MB/s (Transcend SDHC 4GB is unreliable, avoid)
Hub: 4 port one that came with the Rock Band kit for xbox 360