Beware is right, but as long as it is known to the developers etc I have found it isn't too much of a problem.

I have had to mix collations on a sql 2000 server (Binary sort order server with dbs, plus a single non case sensitive db). Once you remember that tempdb is case sensitive etc it is not too much of a problem.

This has even had the bonus of helping enforce naming standards since tables in the other DB's and tempdb need to be exact.