Major lag hit the PC version of Battlefield 3 yesterday: just about anyone if not everyone playing on a ranked server would experience severe and frequent lag spikes coupled with framerate drops, making the game pretty much unplayable. Today the issue still persists.
Speculation says the issue could be due to Close Quarters being available for everyone as of yesterday.
Developer DICE has since indicated via Battlelog they're aware of the issue and looking into it. With any luck, it will be resolved sometime today. In the meantime, play on unranked servers, or use the downtime to actually play a single player game for once (crazy thought).