Does any of you periodically hop brokerages to get sign-up rewards (e.g. cash, free trades, etc)??

some brokerages offer very handsome sign-up bonuses, and if you just request your shares and notes to be transferred, you don't really lose out on anything (maybe a few days of trading). Any thoughts?

for example: assuming these bonuses will be there in the future, rotate your assets among tdameritrade, etrade, and scottrade every year to get cash bonus and free trades?