RoR is one of the most wonderful languages/frameworks to work with. It just works is right...
However, I would greatly disagree with the speed issue. It is true that the environment is slow when working in development (since it needs to reload all the data, functions and code everytime) but when you switch out to production and testing, the systems speed greatly leaps forward. Its blazing fast when it is done right.
If you're not soing anthing more complex than serving up some pages with a bit of data extracted from a database, then Rails is just fine, speedwise. But if you try to do something a bit more processor intensive, your app will bring the server to it's knees.
For example, a while back, I wrote a sort of proxy server. Basically, you directed your browser to my server, and entered in the address at which you wanted to start browsing. My server would download that page, change all of the links so that they pointed back to my server, with a parameter indicating the original link's target, and then served up the modified page to the original client (it was for a game - I wanted to be able to insert news articles onto the NYT front page for example...). Rails was fantastic for getting this up and running quickly, but I couldn't handle more than about 5 clients at once on a reasonably decent server. I had to replace all of the HTML analysis code with code written in C to get a decent throughput (upto about 50 clients simmultaneously without too much lag).
Note, I still use Rails for most of this app. It's just that everyone should be aware that if there are any computationally intensive tasks to be done, you should be prepared to have to recode those sections in C. What's nice though is that you can launch before having do the rewriting - it's a rare site that has more than 5 simultaneous clients from day 1
