This is an excellent little plugin - hardly any increase in load time for my blog.
My biggest disappointment is that it doesn't work very well with Opera - 'the totally awesome browser that hardly anyone uses'.
If you paste FROM Opera - there will be no link.
If you past into Opera - it pastes but nothing is visible in the visual editor (but is visible on the page when you save it).
Oh well; not many smart blog owners out there using Opera anyway, so I guess this doesn't matter too much.
More important is IE (which most people know is a total pain for web masters, because it doesn't adhere to web standards).
Unfortunately 70% of the public still use it, so until such a time as either Microsoft comes to the party or the public get educated, having plugins like this working correctly in IE, is fairly important.
If you copy from another blog using IE browser, no link will be appended.
If you copy from a blog; using a standards compliant browser like Safari, Firefox or Chrome, and then past INTO a page in IE - everything works.
Hopefully MOST intelligent blog owners will not be using IE anyway, so this also is probably not too important.