One of the reasons I don't tend to worry about ideas is that I've tended to find that I have more than I know what to do with or will ever use in my lifetime. I have ideas every time my brain gets prodded by something, and then I forget them 3 minutes later unless something about them makes them stick for a bit longer. I used to worry that I was losing valuable ideas and that I'd run out, but there doesn't seem to be any danger of that.
I remember seeing an interview with Neil Gaiman where he said that it's incredibly common for people to come up to him and say "I have an idea for ...". He said that his internal response was that anyone could have ideas, the hard bit was sitting down and making it into a book/comic/film.
I have a similar memory problem, however, with journal entries. They occur at inopportune moments, like when I'm on a train, or at work. I suppose I ought to get a dictaphone or something similar, but the ideal option would be a laptop. Or not having to be at work/on a train at all, so I could just write.