Since the beta went public, I've noticed a few responses which seem solely to be advertising a particular product, or in one case, the product written by the answerer. While I have no problem with commercial software, it feels like we should identify a line in the sand. I'd say directly posting your companies interests when the response is not warranted (they asked for a cheap or free option, yours is expensive) is too far.
EDIT: The stackoverflow FAQ has been updated with a pertinent response:
May I promote products I am affiliated with here?
The community generally frowns on overt self-promotion and tends to vote it down and flag it as spam, so be careful. Post good, relevant answers, and if they happen to be about your product, so be it. However, you must disclose your affiliation with the product in your answers. Also, if a huge percentage of your posts include a mention of your product, you're clearly here for the wrong reasons. Our advertising rates are quite reasonable; contact our ad sales team for details. We also offer free vote-based advertising for open source projects.