I'm not sure if the faster cards are 'pro' cards or not, but the faster speed is definately not a gimmick. However, the camera you're using will determine if the extra speed actually makes a difference, and that has mostly to do with shooting in 'burst' mode. The more frames per second combined with the increased file size of larger megapixel cameras makes the transfer speed important if you want to keep the rapid-fire shooting going. But it also depends on how fast the camera can move the data. On my D50 I use a normal 1 gig SD card, and on burst mode I can see the camera writing a couple of frames after I stop shooting, but it doesn't slow me down because the camera's buffer seems to be fast enough to let me keep shooting even if the card is a bit slow. But... I'm sure a faster card would let me shoot more frames at full 2.5 frames/sec before slowing down, yet it doesn't affect my use of the camera on a practical level.
Also, I guess the faster cards may download a bit faster, but your card reader also has something to do with that (not all USB 2.0 card readers are truly capable of high speed downloading, which came as a surprise to me...)