Spin Classes?

What do people think of spin classes as a way to improve cycling speed 
over the winter?

I'm hoping that spin classes will help me get faster since they seem to 
be pretty good interval work and the bikes seem pretty close to road 
bikes. I like the bikes a lot better than the typical "exercise bikes," 
and the instructors seem to do a good job of pushing me.

--Harold Buck


"I used to rock and roll all night,
 and party every day.
 Then it was every other day. . . ."
      -Homer J. Simpson