I recently blogged that I was spending more of my spare time writing than coding. That's not just due to Stack Overflow, but it's part of it.
Is that a problem? If so, it's certainly my own fault and no-one else's. Having recently read Malcolm Gladwell's Outliers, I'm beginning to wonder whether my strength/talent is more in explaining things than in actual coding. That would in some ways be disappointing, but would suggest that I'm using my time reasonably wisely at the moment.
Of course, the danger is that the more time we spend answering, the less time we're spending learning future answers. Maybe if I didn't spend any time on SO, I would know WCF or the Entity Framework by now, for example. There's certainly a danger of continuing to answer after your knowledge has become stale. I think it wouldn't do me any harm to go back to coding a bit more every so often.
Questions like this are good for at least prodding us to consider such matters.