Its not as big a deal as people claim, but many people here live in a black and white, 'UR DOIN IT RITE/UR DOIN IT WRONG' world, where things have no degrees inbetween.
The keyboard turning thing isn't a huge deal in PvE, AS LONG AS you use strafe graciously. The reason people don't like keyboard turning is because you turn slow. With strafe, you don't need to turn nearly as much and still be facing the mob enough for combat.
PvP, its a bit more important. In BGs, its usually not a huge deal unless you're going 1v1 against someone, but BGs you're usually fighting against lower level PvPers anyways(not always!) (and before you say it Theo, just because a Porsche is a really cool car, it doesn't mean a Hyundai isn't also a car!)
The ability clicking is a bit more of a handicap. Rogues have to be able to do certain things with quick reaction time. For your normal SS, SnD, etc, it won't make a difference, but if you want to be a good rogue, you need that kick/gouge/vanish/blind etc button right there.
In summary, PvE, you probably will be viable keyboard turning and clicking, but you could be a lot more skillful if you learned to do it the opposite. Its an area that a bit of practice could give you good results.
In PvP, it just depends how serious you want to get about it. PvP is a case of optimal or lose, so think about doing every little improvement you can.
oh and P.S. I find its more important for my hunter to use the mouse to move and keys for abilities than my rogue. :P
Edited, May 8th 2008 9:58am by digitalcraft