Awesome idea, but buggy Rated 3 out of 5 stars
I really really love what Blank Canvas dose. The way it deals with email signatures far surpasses Gmail's built in abilities. Things I love about it:
It removes old signatures from quoted material
It automatically applies the signature appropriate for the current email alias being used
It allows for many different signatures
Unfortunately, there are some serious issues:
1) On occasion, when attempting to reply or forward messages, Blank Canvas will erase the entirety of quoted material. Firefox must be restarted to restore functionality.
2) And the real deal breaker: Blank Canvas uses way too many CPU cycles. I am using Windows 7 64 bit, and Firefox 3.6. I have a 2.4 GHz Core 2 Duo cpu, and with Blank Canvas enabled and Gmail opened in any FF tab, FF always uses between 10 and 20% of the CPU (that's 20-40% of one core, which is all FF can use anyway). If I leave Gmail open for a long time, FF will go up to a solid 50% of total CPU until I close the Gmail tab and reopen it.
So the functionality is awesome, but I just can't use it as long as it's so CPU hungry for such a small task.