As it stands, we have only tested extensively with SQL 2005 Express.
We have experienced no issues of any kind, other than the problems with firewall config etc associated with the stricter security of SQL 2005 itself.
What plans have you got? I can certainly help out if you want to migrate your MDP to a SQL 2005 back end.
Plan? That's a four letter word around my office these days!
What I'm looking at is an upgrade from SQL Server 2000 Standard to SQL Server 2005, but with no definite date yet. I'm sounding out the vendors for known issues or deal killers before I make the plunge. So, yes, this would be a back-end migration for MDP (it's running on the SQL server itself).
I'm not pushing the idea myself, but I am hearing noise from the developers, who have apparently read the release notes for 2005.