They did this at my uni for the ever-pointless student union committee elections. Voting figures were so low (~3,000 votes out of a total student population of 25,000) that they offered free beer and chips. Voting figures jumped to a massive 4,500, iirc. Trouble is, like most students, the young voting population just don't give a damn because they feel their vote won't make a difference (and if it does, the elected then won't listen), and gimmicks are not going to make a difference. It's the whole "motivation by pizza" way of thinking (see: http://tinyurl.com/wcssw)

Also, could it also lead to escalation where successive governments have to introduce bigger and better incentives? I imagine it might get a lot of people to vote if in 20 years' time they're offering free cars or a night with Ann Widdecombe as a vote-sweetener <shudders!>.