I have seen a number of Tallboys at the races, and I plan to race mine. Earlier this year I raced on a Stumpjumper FSR 29er, and I don't feel like it held me back much. As someone said, it's more the rider than the bike. The Tallboy is lighter and climbs better so I'm sure it will be even faster.
I have the stock SPX build on the Tallboy, and I also have a Niner hardtail with Crest wheels. I'll use the stock wheels with burly tires for trail riding and the Crests for racing.
As someone said, if you want a capable trail bike that can also be raced competitively, then the Tallboy is a great choice. If you want a pure race bike, then a carbon hardtail or a Blur XCc or an Epic might be a better choice. The Epic is also a nice trail bike, just a little more race-oriented than the Tallboy.