It would seem that this is an issue that keeps arising again and again and is not really an issue when you look into it. In my opinion any language scales as long as the people who are using it are technically capable. Yes it may be slower than some languages but it also provides some pretty cool features that allow you to code much faster, distribute over many machines and shard data much easier than others would allow (specifically the framework allows/disallows this). It also really depends on what the application is meant to be doing. If I required a lot of intensive processing of data then I would personally go down the Java et al route and do a little mix and matching to find the best tools for the job. Others might use it for both and have proof that it works fine. For creating web apps in an extremely fast time is what Rails is all about. I have written a well balanced (I like to think) article before looking into the pros and cons of rails so take a look if you want to at Rails Scales (Or Does it?)