Gems - Performance Issues

How does the number of plugins/gems used in an app affect overall app
performance?

Thanks!

The main thing you will probably notice is app startup time,
especially in ruby 1.9.2. The require function in 1.9.2 gets
significantly lower with the number of directories in the load path
and the number of already required files. 1.9.3 is miles better in
this respect, and in either version makes no difference once the app
is up and running (still annoying in development though). You'll also
use more memory, the more code you have loaded (although the fact that
it's in a gem rather than being your code makes no difference)

Fred