I've been riding tubeless since 2009. One flat in ~17K miles, and that one could've been avoided had I not hit a sharp rock going around a curve. I love the way tubeless feels and handles. Most of the tubeless miles have been on Campy Eurus 2-way wheels, but this year I'm switching over to Mercury alloys with Stan's tubeless conversion.
Last season was my first time racing. Did 6-7 races. An acquaintance of mine also uses tubeless...training and racing.
One downside to tubeless is the rare time you have a flat. You will have to deal with the sealant. It's just messy and adds difficulty to the tire install. I now carry a blue shop paper towel in my seat bag. If I have another flat, I'm ready.
Another possible downside is if you want to use carbon wheels. Last time I looked, there are only a couple carbon rims designed for tubeless. It's not recommended with the others, although I'd guess it can be done. Under hard braking, there's a possibility of heat deforming a carbon rim enough to lose the seal.
If you go tubeless, I'd recommend a 23mm or wider rim paired with a 23mm tire. Superb feel and very grippy. Great crit setup. Last year I did this for a few races: I used the Mercury alloy wheels with Stan's rim tape. Hutchinson Fusion 3 tires for both training and racing. Run the PSI lower than what Hutchinson recommends. I'm 173 lbs and use 85-90 PSI.