How fast do motorbikes accelerate?

It depends on the bike. Most modern 600cc sportsbikes will reach 100MPH in a little over 6 seconds, the 1000cc bikes will do the same in around 5.5 seconds. 0-60mph usually around the 3 second mark.

The current king of acceleration is the 2008 Suzuki Hayabusa, 0-60 in 2.8 seconds, and 0-150mph in 10 seconds.