I spent a night in Krabi Town on my way back from PhiPhi Island (don't go there, it's a tourist trap and a bit of a shit hole) before heading to the airport the next day for a flight to Koh Samui. I agree that it's pretty dead, but I had a cracking night out there, started in the hostel bar playing beer pong with a pretty sound group, then out of the bar and on to a late night boozer that played reggae tunes non stop. Pulled a Welsh girl who had just arrived after being delayed for a full 2 days, first getting out of the UK and then getting held up at each stop on her connecting flights. Her and her pal had booked in to stay in Krabi Town for two full weeks then home, I suggested they went along to Ao Nang as they'd be bored there within 3 days... Great wee shag she was!
Climb the hill at the tiger cave temple, the 1,200 odd steps are quite the effort (hellish steep), but the view at the top is spectacular and you can see for miles in every direction on a clear day. The emerald pool and hot springs are also worth a day trip out of town as well!