Half a second input latency with everything. Literally. Even the Steam overlay.

[Alex]

This should be what it says on the tin, as I literally can't play the game like this. To be fair, I do have a 10 year old laptop. And its not a top-of-the-line gaming laptop from that time period, either. It runs Portal, Portal 2 and Portal Stories: Mel just fine.

[Alex]

Update: The input latency in the game has significantly reduced to the point where I can actually play the game normally, but probably not perform insane portal tricks.

[Alex]

Update 2: The input latency seems to be related to lag. When I'm in a chamber with stairs made out of floor panels, it takes more time for a flick of the mouse to register than in (for example) a replica of Portal 1 test chamber 00.