So far the PLA has been working very well. My only complaint is that it is very shiny, which sometimes makes it difficult to see small details in a model. However, the overall look is very nice, especially for the more translucent colors.
You can get spools of PLA filament from many places online. Our Replicator 2 takes 1.75mm filament so we ordered some 1.75 filament from amazon.com. It works fine in the printer but the spool does not fit on the Replicator 2's spool handle. Nothing that can't be fixed with a pencil, rubber bands, and a box, though:
Of course, with a 3D printer one could also print a smaller spool holder:
Here's a hint about changing filament in the Replicator 2: Through the "Utilities" menu you can select "Change Filament" and then either "Load" or "Unload". The "Load" function heats the extruder and then runs the motor forward; you push the filament through until it starts extruding. (Basically this machine is just a giant glue gun, so if you've loaded a heated glue gun then you know how to load the Replicator 2.) The "Unload" function runs the motor in reverse so you can pull out the filament. One time we could not get the filament to pull out during the unload process. Under the assumption that maybe the filament had made some kind of ball or obstruction that we couldn't pull through, we ran the "Load" function, let it extrude for a couple of seconds, removed what was extruded, and then ran "Unload". It worked great and now I do all all unloads this way, with a quick "Load" to start and clear out anything that might be in the way.