well, i was used to photoshop before, but as we all know, there wont ever be a version for linux. and because gimp is very similar to ps in most regards, i tried it and was happy. the best thing is, that they are constantlyy working on it, making improvements and stuff.
and yes, i have a tablet. and you are right, without it i wouldn't have been able to draw the warf... but you get tablets for nearly no money theses days and most off them are not too bad (but also not as good as the wacom thingies... i loves me my graphire 3 8x6).