Weapon Focus: <slashing weapon>, Dodge, Mobility, Expertise, 3 ranks each Tumble and Perform: Dance, BAB +5. (Length of Dervish Dance is perform ranks/2 so max ranks is a good idea).
That's a lot of prereqs.
I like that Dervish has several cool abilities... I actually created my own PrC with the "may full attack while moving but must move at least 5' between attacks" mechanic before complete warrior came out, so when I saw Dervish, I knew I'd have to play it eventually.
I really wish Dervish gave two weapon fighting feats as bonus feats. Add two weapon fighting to the list of requirements, and give improved two weapon fighting at first level, greater at 6th, to make up for the fact that the class requires a very feat heavy chain, and doesn't give any way to get those feats.
Hrm... not a bad idea for a request to my DM...
-The Souljourner