I do randomly enter competitions , but they have to be the ones that require very little effort from myself.
My daughter entered a Sony competition where you had to send in a quick video of yourself doing a mexican wave , and she won a week in South Africa, for the 2010 WC, including flights and a 5 star hotel and tickets to one of the QFs.
It turned out, they only had 52 entries in total.
So, the more work you have to put in in entering, the more likely you are to win, as they will have very few entries.