Well, it might be.
Now that everyone, every brand, every organization and just about every person is in a race to build trust or an online following or a reputation, the question of working for free in exchange for exposure confronts us all.
Should you art direct a new ad for the local zoo, merely to build your cred? Should you give that speech for free, because people who pay speakers will be in the audience? Should you contribute code to the new kernel because people will see what you've done? Appear on a talk show, do a signing, call in to a radio show?
Unsatisfying, but true.
Exposure, the right kind of exposure, is good practice, an honest contribution and yes, a chance to build credibility. Make it a habit, though, and instead of exposure, you've set yourself up a new standard– that you work for free.
Alas, one more decision you need to make.
Some designers (and authors) violently disagree with my case by case approach… they think the entire profession is cheapened by spec work and work for exposure–they argue that solidarity is the only response. I'll point out that these very designers belong to organizations that ask speakers to speak for free… for exposure.
If you're an unpublished author, you're certainly better off doing a lot of writing online (even entire novels given away) for free before you veer in the direction of doing it for a living. In fact, most people I know (in every field) don't do nearly enough work for free, they're not contributing enough to their community, not adding their expertise or their ideas to the conversation. As a result, they're either invisible or seen as not interested.
Punchline: just because it's free doesn't mean it's a good idea (or a bad one). It means you should think hard about how everyone benefits (including you). [PS a video from last year you might enjoy, complete with Y! tie.]