A while back I played a small points game (around 1000) against Jester. He broke out some Tau and I used my Orks and we had a go at it.
Jester fielded a heavy Crisis Suit list along wtih a few tanks, a few units of Firewarriors, some Kroot, and some Pathfinders. I was fielding some Killa Kans, a Deff Dread, a Warboss on Bike with Nob Bikers, and two units of Trukk Boys.
One of the first things I realized is how maneuverable the Tau are. Jester set up as far back as he could, and I set up as far forward as I could. I had played the Tau before (but only a few times) and I knew they were fast, but Jester really worked these guys and kept every unit highly mobile and jockeyed for position - planning moves a turn or two in advance.
As I moved towards the Tau he would pull them back or retreat them laterally away from me, this let him keep getting shots off while keeping me out of combat range. The Kroot served their purpose to a T - screen units to keep them from getting assaulted, and serve as a speed bump. By sacrificing Kroot or even a small man unit of Firewarriors this let his Crisis suits and tanks get in an extra round of shooting - which is really all the Tau have.
Something else that I hadn't really felt the sting of before was the massed marker lights from the Pathfinders. Getting on average 2-4 hits with these guys can really swing the shooting phase. Jester was able to lower the cover save on my Nob Bikers by two and increase his BS by 1 on one turn - this had him hitting on 2's and 3's with his command unit and left me with a 6+ cover save from most of the shots.
As the game wore on it became evident that the Tau were just out gunning and out maneuvering me. My Nob Bikers with Warboss were wrecking everything they got close too, but I wasn't able to charge two units at once because of the crafty Tau and their Assault Phase movement coupled with screening units. This left me hung out on most of Jester's turn and I was slowly picked apart.
The game went to six turns and in the bottom of the sixth I was tabled. All Jester had left on the board was a Tank, some Firewarriors, their transport, and one Crisis suit. It was a monumentally bloody game.
The biggest thing that I took away from this game is that you have to be very purposeful in your movement against the Tau. They are able to react and redeploy so fast that you can't haphazardly move your units around. You also have to watch out for their tricks - fletchette launchers, fail safe detonators, and all their other weird wargear might not look that impressive on paper, but a good general can stretch all kinds of value out of them.