We use it on one of our webhosting servers...with mod_fastcgi (which is a must). Can't say if its worth installing.
We have one customer (reseller) that's using it on maybe 15 websites so I guess it's worth it for us...it was pretty easy to install. Besides the reseller, we haven't had any new customers wanting rubyonrails in about 9-10 months since we installed it..in other words: we wouldn't have installed it for only one user
I did a few stress tests on the server with a customers app...a "standard" website with a few database functions...worked OK but it was a bit more CPU expensive than PHP.