Seconding everything Hood said and adding that USB power caps at something like 500ma (per port).

I can't speak for all computers, but my laptop's reaction to drawing too much power was to simply SHUT OFF the juice to the port!  Not pretty.

PC power supplies are regulated very well, methinks and they are dirt cheap. I'm using an old one that can no longer run a motherboard, but still puts out a nice steady 5v and 12v. You can just jumper the 'ready' or 'power good' (per Hood's post) pins on the motherboard plug and the power supply will switch on a and run by itself.

I saw somewhere that the common wire for the 5 volts and the steppers power should be the same.
Does that mean I can't use two seperate power supplies, one for the 5 volts and another for the steppers?
One more thing, how much tollerance with the 5 volts have I got. The computer power supply I have seems to pt out 5.5 volts. Will that fry the SS or Geckos?
Could that mean the power supply is on its way out?

BTW can a moderator please delete all the previous bullsh1t posts in this thread, as I havnt been back long enough to warrant the afterhours, let your hair down and play with the lads stuff.

I think it is normal practice to have all of your 0V connected to provide a common reference point,  whether that be from 2 different  5v supplies or a 12v and a 5v etc unless I suppose they are on separate sides of opto isolation. Then again I am no expert at this so maybe wait for someone else to chime in.
Usually computer PSUs have a tolerance of 5% or less, your seems to be nearer 10% but I presume that is unloaded, if you put a load on it will probably come closer to 5V. Cant remember exactly what voltage Greg said was too much but its definitely on his forum if you do a search, think 10% should be acceptable but less would  obviously be better.

Hood