I've had my Tau for a few months now and I've some some success with them. I've tweaked the list a few times though. As people were telling me, I used Kroot for a bit but they never seemed to do much more than dieing so they were back out of the list. I did drop a devilfish and give the Pathfinders' fish to a Fire Warrior squad and I'm now running a Warfish set up and it seems to be working better, the extra shots and BS turn these guys into suprisingly nasty tanks. Wether or not I keep them that way remains to be seen becase this development is fairly new.
Its just a shame that the Kroot didn't work out for me, because I love thier fluff :(