My personal opinion would be to NOT try to fill the seams in paneling. I've done & seen a lot of painted paneling, and in my opinion it looks just fine.
Unless you are absolutely awesome at filling the seams (which most DIYers are not), it's going to be obvious that you just painted paneling. So let it be obvious.
I'd like to clarify something.
I painted the paneling in our last house. I agree that painted paneling is gonna look like painted paneling and trying to make it look otherwise is pretty much pointless.
That said, I would recommend filling the seams between the panels (every four feet) and along the trim with paint-able caulk. Otherwise these can show as fine dark lines against a white or pale paint. BTDT.