You can pre-populate a tweet by doing something like: twitter.com/home?status=I am asking a question on stackoverflow
If you want to use a hashtag you have to urlencode it http://twitter.com/home?status=I am asking a question on %23stackoverflow
If the user is not already logged into twitter, once they do log in, they are redirected to a 404 because of these hashtags. I am sure its because twitter has to save/pass through this status query string while you log in.
Any one have suggestions? A hashtag is important to me in this situation.