Rated 3 out of 5 stars
When it works, it's a great plugin, but it's very flaky for me (1.12.06b )
At first, it had a bad habit of "forgetting the signatures and I'd have to type them back in.
Lately, I just can't get it to show in GMail at all.
In general, I think this functionality is simply difficult to pull off with a browser plugin and it really needs to be a GMail Labs add-on