Some installers like to not have the baseboard down before the carpet, others (like Sirquack's) like it baseboard first.
In my basement, which is a never ending project, I have no baseboard, or any trim in so far. We are trying to finally get the bathroom done (almost ready for the plumber to come back and hook everything up), get some shelves up in a closet, and finish my home theater equipment rack (I need 3 pull out drawers yet). I did, however get my star ceiling done and put up tonight, so I am getting there. Anyway, you may need to check with your installer as to if they care if the baseboard is on or not anyway. And as Sirquack said, if you do it before the carpet, you must leave an even gap between the uncarpetted floor and the bottom of the baseboard to allow for the carpet to be "tucked" under it.
