I have a Makerbot Replicator 2X 3D Printer. It can print in both ABS and PLA plastic filaments. So far, the only plastic I can get prints out of fairly reliably is ABS.
I found some interesting info on the subject in Google Groups:
I tried some things I saw here with some slight improvements. But it is still not worth my trouble.
I am giving up printing in PLA for now, I will probably try different things every now and then when my patience is running higher.
We will see.