I got myself a pup while down here in PCola, and will totally agree on the above statements about neediness especially with a working dog like a GSD. Everything said about time above is 100% true... but in addition to that you seriously limit yourself on housing options... With a gsd you will HAVE to have a BIG privacy fenced backyard and will most likely have to work on the fence so he/she cant dig under it. Plus, a lot of places limit dogs to less than 50lbs which your gsd surely isn't. The, finally, when all is said and done and you've found that magical house that fits all those needs... BAM, $300 pet deposit, extra $25 a month to feed them, vets, dog house, chew toys, replacing objects that the dog decided were "chew toys", etc.
OTOH, the companionship is great. You can't take your cat out for a run, and unlike a GF/wife they will always be happy to see you come home. I actually enjoy running with my dog, even though I hate it without.