Hm... Lava does sound effective, but a griefer who's on his toes would be able to act fairly quickly against it if he's got tools handy. I personally prefer minefields, although its close to impossible with the Beta to cover up your minefields with snowy land/etc to use as cover. This looks like a nice alternative though.
I realize this is just to show the concept, but it would be far more effective if the lava wasn't right there where it was so visible. Also like others have said the redstone trail needs to be hidden. Personally I'd just use tnt, but this design might do less damage to your home in the end.
new griefer trap extremely effective