@rodbegbie, you’re totally right.
We’re going to start by implementing this as an option for new-style RT’s only.
And I think if the users don’t choose to filter them, we will still change the construction for Facebook (e.g. change it from “RT @username: message….” to “…message /via Real Name”
We will leave conventional RTs (i.e. regular tweets leading with the construction “RT @username”) unchanged.
How does that sound to people?
This is probably a higher priority item for me than anything else (including translating links and images, or excluding hashtags). I don't use the old-style "RT @username" at all. I will typically re-word the post or quote it directly, and then give the user credit at the end (e.g., "/via @username"), often with my own comment after that (e.g., "[I need this]"). In this way, the tweets I create are still very appropriate for Facebook.
When I use the twitter retweet option, which does not allow me to edit, just to endorse someone else's post in my timeline, it gets translated into "RT @username" and looks clunky in Facebook. I would much prefer an option to ignore all Twitter retweets as a rule.
+1 to Steven_noble's three-year-old idea to give the translation to Facebook an option on how it deals with hashtags. Hashtags are used in many ways, so my guess is that no option would be able to translate all of the hashtag uses 100% correct for everyone, even with more control over settings. However, it would allow people to use the service to reflect their primary use of #hashtag.
As a rule, I don't like hashtags anywhere. I tend to use them sarcastically on Twitter, so I'm not expecting them to lead anywhere useful (i.e., link to a twitter search). I probably would experiment with controls a bit, and then just go back to letting them into Facebook again.
This is an important part of recognizing the difference between Facebook and Twitter cultures, which Tweetpo.st aims to do.