It's the second time today that I have a teammate refuse to surrender because it "halves IP gained." I can find no source confirming this, so I doubt it is true but I thought I'd make sure.
There is no "penalty for surrendering," but IP gain is linear with time (up to a threshold: 55 minutes), so the longer you stay (even if you're losing) the more you can gain.
That said, it is often faster to gain IP by surrendering if you believe you have a good chance for winning (eg. 50%)