I've been using this for about a year and a half now. It's much better than running the whole bloated Last.fm software (which I have to say is really awful), but lately iScrobbler is going downhill too. I've been having a problem where it keeps queueing tracks for submission, but it won't actually send them until I quit iScrobbler and relaunch it. That's been happening since the last 1.x version; now we have "2.0" with a useless new "local lists" feature that seems like it will take a week of CPU time to finish computing its stats, and meanwhile that submission bug is still not fixed. Now in the last couple of betas, we have lost the "Statistics" menu item, so now I can't even tell how many tracks have not been submitted anymore.
Meanwhile, the "loved/banned" feature has never really worked properly. After you add 10 songs to either of those lists, it stops letting you add any more. The UI has some major problems in that area too.
iScrobbler seems to be getting worse with every release. I hope they turn it around soon. It used to at least be a good, lightweight tool for submitting tracks in the background, until that stopped working reliably too.