Yeah, cross platform play is going to be brutal for console players. It works in Portal 2 because you're working together, but if you're competing against a person who can aim 10x as fast as you can, you're in trouble.
Nevermind the fact that there's pretty much no way to make the buy menu remotely as fast on a console, so there's another disadvantage. >_>
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Falcon Punch
http://www.youtube.com/watch?v=FFtw7qW7Vcw