I assume you're asking about scalability in terms of pages per second or whatever, but what you should be more worried about is the scalability of your developm

I assume you're asking about scalability in terms of pages per second or whatever, but what you should be more worried about is the scalability of your development effort. As other posters have said, speed of the platform is not the issue. Rather you should consider what platform you think you can get the most done in the shortest amount of time - having friends that use the same platform counts for a lot. Similarly, many people think (including myself,) that you can get more done faster using RoR or Django than you can PHP, particularly if your project has any complexity.