Active speakers, if done right, can be really great. Those of you who have been around for awhile might remember the Powered Advent speakers of the mid- to late-70s. These were basically the same speakers as regular Large Advents (actually the "New Large Advant"), with a simple 2-way acoustic suspension design. But, they had a pair of amps built into each speaker, so you could drive them directly from a pre-amp. They were essentially giving you a bi-amped set-up. The improvement in sound over the regular New Large Advents was pretty substantial.
A current high-end example would be Meridian speakers, which take active speakers the further step of being "digital bits in, sound out". These sound great, but are not cheap.
The main arguments for integrating power amps with the speakers is that you can then tailor the size, frequency response, and gain of each amp, so that it is optimized for its specific speaker driver. If you are just putting a single amp into the speaker cabinet, and using it to drive all of its drivers, then the advantages are much less.
