I've spent some time developing a little Android app to scratch my own itch. I'm considering publishing the current version as a beta in Android Market. Pros for publishing it now would be the potential to get feedback. It would also be a way to gauge interest in the app which could effect whether to develop it further at all. What would be the cons of publishing beta in Android Market?
The only cons that come to mind are potentially tarnishing perception of the application (or of yourself as the developer) if it's poorly received and/or buggy. Only a very late beta should really be published in Android Market, if at all. If you want to gauge interest or have users do actual beta testing, make the APK downloadable on your website or Github, etc.
This reduces your potential audience (to people who can enable the install of non-Market apps), but it's still a pretty large number of users who have this capability, and you might get better testers.
That being said, if you just want to get it out into the wild, are fairly happy with it, and aren't using a developer account you ever plan to sell software on, you don't have much to lose putting it up in Market.
There's also a discusson here about publishing beta apps from the android-developers Google group.
Imagine that you want to buy an app from Market. You enter some keywords and get a list of apps, sorted by rating. Some of them are free. What you pick first? Second? Probably not something that has average 2.5 stars and a lot of negative feedback. You probably stop looking before you get to 3-star ratings.
But a lot of negative feedback ("Force closes all the time!", "Lacks X, Y and even Z, useless") is what you get if you publish beta-quality software. It's easy to get initial negative feedback and low rating, and very hard to change the situation afterwards, see paragraph 1.
The only case that I can see when a beta-quality app is worth publishing is when it's something totally unique and unlike anything else. You can get earlier feedback without fear that competing apps will attract your users. If your app is like that ("The only teleportation app on the market!"), you can try. But be sure to add a big fat BETA VERSION disclaimer early in the description, so that people won't mistake it for the final product.