6500k CFL's are great for vegging as long as you are not growing trees, they are also great for side lighting. You have already mentioned the 2 main advantages (less heat and electricity).

The biggest disadvantage of CFL's is poor light penetration (hence the tree comment) which makes them less effective during flowering. They can add 2 or 3 weeks to your flowering time.

I have a friend who grows with MH/HPS, he borrowed two of my 125w CFL's to veg for his last grow (he normally uses his MH/HPS lighting) as he wanted to veg while his grow finished flowering. He has now cropped that grow and he got his best yield ever. I don't think vegging with CFL's increased his harvest, but it certainly didn't decrease it. He is going to borrow them again.