Some time ago I wanted to enable some features upon a siteCollection creation, but I couldnt find an eventhandler which allowed me to execute those actions. You could, of course, add or alter the ONET.XML for a new Template, but if you need to run code/activate features on Site Creation for multiple...
I would like to reference to an old post that appeared in 2007 on http://blogs.msdn.com/sharepoint , that mentions the SharePoint debugger feature. I use it quite a lot and i am sure a lot of people don't know about its existance. Its a relatively simple feature that shows up in the SiteActions menu...