We've seen pools with 6 times (or more) the current difficulty before finding a block. In other words, you could spend 150 coins to receive 25. Or you could get 25 coins with a 0.20 investment. It is a simple gamble, not a way to make guaranteed profit by any stretch of the imagination.

So as to how profitable? It can be wildly profitable, but it will most likely be a losing prospect over time due to fees involved.