I do use RSpec, but I have some of the same reservations as Courtenay. This is really a more general problem with any third-party library: using gems, plugins, etc. can give you a big leg up if they provide the functionality you need, but they also represent another point of failure.
I sometimes get frustrated when people say "Why not just use 3rd party library X?" I'll tell you why: because it will eventually break.
I think this is more of a problem with ruby gems then 3rd party libraries in general. Maintaining gems across dev/test/prod environments is probably more complicated than just packaging 3rd party source with your app.
It's certainly possible to package gems with the app, but I don't know of any established best practice for it.
If you're on rails, it's rake rails:freeze:gems. If you're using Merb, you can use frozen-merb. If you're just using some adhoc ruby script, you can always install your necessary gems in your home directory in .gems or something and symlink that whenever you need it.
It's not that they stopped, it's why they stopped. Reading the comments sheds light on even more problems with rspec and options for other testing stacks.
I sometimes get frustrated when people say "Why not just use 3rd party library X?" I'll tell you why: because it will eventually break.