[eluser]Dam1an[/eluser]
Have you tried looking through some of the PHP forums on SourceForge? Even if they're not MVC/PHP, you could get some ideas from them. It might help you finalize exactly what you want, and methods etc
Returning a collection of threads wouldn't complicate things (or where you thinking of having it in a seperate method to get threads in a forum?)
As for the get_thread($id) vs get_thread_by_id($id) I was just showing how some names can be unnecesserily long, as you correectly said you'd assume to fetch it given the ID