Oh yeah, all the time! I actually think that's part of the whole creative process, letting some ideas ferment for a little while, to see if they stick. The worst-case scenario is when you're pondering an idea for so long that someone else comes up with the same idea! Even worse is when you know they did a better job than you could have done.
I try to break the idea into smaller steps and think about what I would do first and then the idea becomes more concrete and either starts to take shape, or is abandoned, or is thrown back to ferment a bit longer.