I purchased the Pro version today, and the rewrites are working fine but when I try to add custom rewrites via the dbseo control panel they simply don't work, have no effect. I've attempted to flush the cache to no avail.
Can you please verify you have set "Force Forum Directory Index" to No? Otherwise, the forum.php -> forums/ rule will not work.
The showgroups.php rewrite rule is working perfectly for me, though I did discover that the Canonical URL enforcement was not active for custom rewrite rules. This will be corrected in v1.0.8, due to be released on Monday