There are definitely things that FPGA's are very fast at, but they usually have pretty specific uses. They generally aren't used as direct replacements for uC's in final development. There are very fast uC's like ARM9's and ARM Cortex if you just want speed.
Someone posted this link a while ago, and it's pretty nice for beginner FPGA.
fpga4fun.com - Welcome
Any site on ARMs? I like to read up on those to get a better idea....