Sure, as long as it's on topic, and not loaded up with links. When I've done it, I haven't put any links in the actual post, just one in the profile.
Thanks for the response. I've actually seen people recommend against this, for fear it will hurt Google rankings. I've been trying to convince myself for two years now that I have to forget about upsetting Google and just work on tried and true forms of promotion that work. Then if Google dumps me anyway, at least I have other traffic streams.
Here's a rather obvious thing to add to the list: offline relationship building. It seems like a low ROI to some people, I know, but people respond differently if they know you in person. While I've gotten tremendous value out of knowing other webmasters online that I'll probably never meet, knowing people offline is really something else.
I keep business cards for each site, and hand them out to anyone who shows interest in my sites. In this economy, I get more interest when people learn that I actually make money running websites - they want to know how they can do it themselves. I've helped a few people get set up, and several of them have rewarded me with some fabulous content opportunities for my site. A lot of people know a skill, like great cooking, and they just need someone to help them see how that gets turned into a website. And once I help them, they want to help back.
I also have a couple of sites that cause me to go to shops a lot and keep track of what's being sold in my market, how it's being merchandised, etc. I've gotten to talking with a number of my local sales assistants in these shops, many of whom have their jobs because they love the products they sell, and they're thrilled to hear I have a related website. Do they all come visit and send me traffic? Not at all, but they know me when I come see them, and they meet bigwigs from the corporate office who might be interested and so on. You just never know where relationships are going to lead.
This is just good old-fashioned salesmanship, which despite what you may have heard is really just listening to people and trying to think how you can help them. I try to do this online as well, but I don't think you can replace doing it in person.