Why are you limiting a post to 120 characters?
I post to Facebook and set Facebook to post to Twitter with a link back. The limit would be much better the Facebook limit if you must have one. Better still is no limit. As soon as you add Blogger support (I can not believe you do not have it yet!) I will post my blog posts through Seesmic too. Blogger post to Twitter with a link back.
I post daily bible verses and bible trivia which goes over a majority of the time on twitter. but our tweeters know to go to our page to see the entire verse.
as for facebook followers, linkedin etc., they are able to see our entire post a majority of the time.
every other network should not be limited just because that is the way twitter chooses to do it. don't you think?