In theory...
 

If the threads, etc are all stored in SQL database.. can I not have multiple servers with different homepages share the same user and forums database??

In theory, yes. In implementation, all hell would break loose. Search and ye shall find. :)

just like communism this is a good idea in theory, but it rarely works

What if I were to ALIAS the forums directory to all these sites?

it's been done

www.techimo.com/forum
http://www.photopost.com/forum/
resellerratings.com/forum

all the same database

By aliasing the forums or just seperate virtual servers querying the same database?

I think you meant to refer more generally to Socialism (Communism implies cruel tyrants). However, Socialism does work.

It's been done (and mostly easily) where forums share the entire database. Sharing just users would be troublesome, let alone forums.

communism is socialism after human nature has taken hold..

socialism is the theory, comunism is the result.

;)

but this is offt topic sooo