I and at least one other person here could use a feature that allows shared URLs to be customized. In particular, adding query parameters to the URLs, though arbitrary alterations may be useful (assuming a simple enough configuration interface could be designed). For my purposes, the parameters depend on the share button (e.g. facebook, fblike, plusone). Global parameters and copying parameters from the current page request would be useful to others.
If ShareThis is interested, I could help with the design & implementation.
On a related note, when the ShareThis plug-in sets a share button URL, it doesn't passing the URL through the
the_permalink filter. This may be by design, or it may be a bug.