Anyone had troubles with opening several ppc accounts

Hi !
Had anyone heard of any, or had themself in trouble by opening multiple accounts at adwords, yahoo, msn or so.
I could imagine you could get your accounts closed, but is that the only risk any one have heard of?

It seems easy to buy vouchers and get almost free advertising, but guessed that google are pissed about that method and maybe has ways to get it stopped.
Hope not!

Thank you