MySQL support is a must in my opinion. Both databases should follow the SQL standard closely enough that the extra work should be minimal. In addition, I'd say that the ability to run with medium trust on shared hosting is essential, so a separate dll won't work. A separate class/module would be a reasonable way to separate the data access layer without requiring a dll.
Throughout the code, there are "DELETE * FROM tablename ..." statements. I don't know about the other supported databases, but the MySQL database only supports "DELETE FROM tablename ..." I've done a find/replace in my copy of the code, but I figured I'd let everyone know. In the future, if the * is required for other databases, there should be a config setting for it.
Re: GoDaddy Hosting Issues (Permissions/Trust/Settings) (6 replies, posted in PunBB.NET discussion)
I've got hosting on hostmysite.com and had a similar trust issue. I was able to work around the issue by enabling remote access of my site's MySQL server, and running the install from my local machine in VS2008. After the install was complete, I copied all modified files to my hosted account and everything works great!
Since Godaddy won't allow remote DB access (AFAIK), you can run the install locally on a local DB, then just edit web.config to point to the correct DB, and copy the local DB to the remote DB.
I hope this helps.