Elation and Frustration

I just finished "Tithe" by Holly Black (review forthcoming) and was struck by a linking theme between that and the Harry Potter books, which I'm listening to on audio (just started book 6, so I'm ahead of schedule). Both of them deal with magical worlds that exist side by side with our own, below the surface, as it were. Now, I have no desire to write a story about a wizarding world (Rowling pretty much owns that space), nor about faerie (not without becoming a lot more conversant in the extensive discourse going on with those worlds--I am familiar with some of it, like Greg Bear's excellent "Songs of Earth and Power," but I never read, for instance, any of the <color> Fairy books, and I am largely unaware of the current flood of YA urban fantasy out there, though taking steps to remedy that). However, that line of thought did give me an idea, which turned into a story, and in the space of a day, I have another idea for a book to write.

This is cool. This is spectacularly fun. Unfortunately, it doesn't get any of the current projects I'm working on finished any faster, nor does it give me any more time in the day to take care of this idea. The good news is that this story is probably a shorter novel than I'm accustomed to writing, and the idea is one of those burning ones (in Greg Bear's parlance, a vibrant new world) that supplies a lot of its own energy.

Now I just need a month off to write it. So what do you do when you get an idea like that? Put it on the shelf and finish your current projects, or dive right into it and figure the others will take care of themselves eventually?