I was in Krabi in March. There's not a great deal of action there compared to other major resorts, but enough to keep you entertained for 3 or 4 nights.
You want to head to Ao Nang for the best action. There are 2 basic hotspots to hit:
Centre Point, which is a small/medium complex hosting around 10 bars, a ladyboy cabaret show, and 1 gogo bar on the 1st floor (I think). This area gets loud and lively as the night goes on, and you'll find a few freelancers hanging about as well as flirty girls staffing the bars.
The other area is soi sunrise (roughly opposite the McDonalds), a smal