With oil based gloss, (if you get to it quick enough) you can lift the excess with a scraper then use white spirits to shift the rest, a nylon bristle brush helps with this, im a painter and decorator and ive had the misfortune of this happening a few times, on one job, my mate spilt a full 5ltr tin of white gloss on a carpet, took us ages to get it clean, the patch that the paint landed on ended up cleaner than the rest of the carpet, so we had to wash the rest as well, the guy who owned the house was delighted, he thought that carpet cleaning was also part of our job.