Their Debian distro should already have a default user and LXDE installed. It's no speed demon by any means, but it should be pretty responsive if you have sufficient power. I was having problems with sluggishness and freezing up until I realized it wasn't getting enough juice. The Pi requires 5v/700mA and all of my HTC chargers put out 4.76v/700mA (even though they are rated at 5v/1A.) That's barely within acceptable tolerances. So, when I would plug in a power hungry USB device, such as a bluetooth dongle or HHKB, the Pi would slow way down or just go totally ape ****. I resolved the problem by using a powered USB hub for setting everything up. Afterwards, with the bluetooth ONLY plugged directly into the Pi, it was stable. If I was to plug a keyboard directly in at this point it would start flaking out again.
Moral of the story, use your multimeter - even if it seems okay.
Got my second Pi from Newark/Farnell today. The packaging was sub-par in my opinion. Just a paper thin cardboard box inside a thin bubble bag. RS shipped inside of 2 heavy cardboard boxes and form fitting foam. The circuit board is slightly different as well. The one from Newark/Farnell seems cleaner, has a Samsung chip instead of Hynix, and it has more markings as well such as a CE mark printed on the board.