Hosting multiple sites via rails - Should I use one rails instance, or many?

I am building a rails app that will host multiple archery league websites. Lets call it myarchery.com, and say I have 2 sites: billsleague.myarchery.com and jimsleague.myarchery.com.

Now when I build this I can either:

Have one rails app serve up the subdomains (basecamp style), sharing all models, etc, but putting an account attribute on everything
Set each account up with its own rails app instance

I prefer running them all in one instance - (B/C I can set their sites up immediately when they sign up, have a single login, etc). However, I wanted to see if there legit reason to run them independently.

I plan to run this on a Linode using apache/passenger, if that influences your answer

Solution

Using rails3, you get subdomain routing 'for free'. See http://railscasts.com/episodes/221-subdomains-in-rails-3.

I don't see why you'd need an account attribute on everything; your normal associations should allow you to determine ownership of subobjects.

Running multiple instances per subdomain might seem simpler, but you will pay a heavy price in maintenance. It just does not scale well.