Thanks for the input. Heres a question. Can a biker unit turbo boost, fire AND assault in the same turn? Or if they turbo boost can they only assault, or some other restrictions? If not, this would allow them to have a 30" assault range...
One thing that hasn't been pointed out is that despite the "low" unit count, their are still an average of upwards 45-50 T5 models on the table, usually boasting either 4+ boost saves or 3+ saves in CC. In addition, they also get more attacks in CC than normal.
For a 10 man FW squad, even at RF, they get 20 shots. Thats 10 hits, 5 wounds and only 1-2 actual kills, on a good, perfectly statistical day. Now if you castle, this squad can easily run into at least two squads, and the chance of seeing one isolated biker squad is low.
What I typically see is the three biker squads moving together, ensuring that cover saves are granted to the majority regardless of turbo boost. Following these are the Attack Bike squads, clearing up "bumper" units like kroot, mauling FW squads and taking pot shots at tanks and Crisis unit squads. Now all this time, the scout unit(which may have combat tactic'd into two squads, is sitting in cover or behind terrain waiting for the objective grab) is maneuvering to either contest an objective or add its, surprisingly, potent firepower to the fight. As if this wasn't enough, the Command squad on bikes is hunting down crisis squads that simply cant run fast enough away.
Some of you have recommended "castling", and the use of kroot squads to get in the way. One problem, though, is that with a 24" inch move and a potential 6" assault, they can afford to just go around you. On the flip side, your never going to be dealing with just one bike squad assaulting your lines. You could have a kroot squad, 5 FW squads and a Deathrain XV8 team as a gunline, and 3 Biker squads numbering 27 models deep can potentially tie up everyone of those units.
Another suggestion (not in kill points games) is the use of cheap throw away units to prevent assaults on your more valuable units. Since you can't consolidate after assault, once they charge the throw away unit then you can knock the bikes out with heavier weapons such as plasma and fusion blasters.
This is ideal, and a tactic I have used in other games. However, in these situations, the unit(say a pair of full size FW squads, or some FireKnife XV8 teams) are typically tied up with the other two Biker squads.
Another tactic mentioned, ie the liberal use of seeker missiles, pathfinders markerlights and vespid looks good but I see many flaws. Namely, you have to first hit with the markerlights. Then, you have to hit with the missiles/vespid. Then you have to wound with said missiles/vespid. THEN you have to hope they fail their cover save(which they will have) or pray you have excess tokens to take away cover save. THEN if you used vespid you have to hope they can survive the ensuing charge. First and foremost, this whole process was a huge point sink, just to do minimal damage to a single squad. If you take a Pathfinder unit, you have to take a devilfish. To bring the required amount of missiles, you need at least two Skyrays, limiting your ability to bring Hammerheads or Broadside mounted railguns. If you included vespid, thats another expensive squad. All these points limit your other tactical options and unit choices, and on top of that, won't leave any room for viable troop choices in sufficient numbers. In objective based games, it becomes an easy grab for the biker player.
What I see as a problem is that, to truly "win" against this army, you have to, more or less, completely wipe out his biker squads. Even a single remaining bike can make a last minute dash to contest or claim an objective. Yet it also seems that other than extremely lucky rolls and decent hits with the markerlights, Tau don't have the weapons to do it. And face it, before you can even consider deepstriking an XV8 team, he has already reached your zone(how many boards are bigger than 4'x4', not barring the fact that hes usually not going to line up all the way across his back table edge. He/shes going to sit as far forward as they can, providing cover is abundant. AND that scout squad is going to be even closer if convenient)