If I were make small apps in rails such as personal blogs etc I read a
post saying that I would only be able to host around 30-40 on a
dedicated server as opposed to around 300 if they were wirtten in PHP.
I was wondering if you would have a similar problem if you used
I don't know anything about django, but... you're above statement is a little misleading....
While technically correct I suppose, it is wrong to assume that you could run 300 *simultaneous* PHP apps on that same hardware.
Usually when someone says what you've said above what they mean is that your apps are small, little used... so by using PHP you can "over sell" the hardware since most of the time no one is requesting pages anyway and if they aren't, the server doesn't have any resource usage as PHP isn't standing around waiting for a request.
With Rails, this isn't true. Rails is persistent so even if you're not actively serving requests, the rails framework is still loading taking up RAM.
If you're app makes good use of page caching (as does mephisto/typo) *and* you use a webserver such as litespeed (i believe fcgi can do this as well) that can shutdown the rails instances after a certain amount of inactivity, then you could host even more apps as 99% of the requests will be to static HTML which your web server can handle without loading Rails at all.
I have a personal blog and a small site for a friend... neither of which gets hardly any traffic. I don't track it much, but I hardly ever see a rails process running on my box as things are either cached or no one is using them.
Anyway, just something to keep in mind...