This is indispensable. Excellent replacement for signatures (which are a bit weak in Thunderbird). Also the HTML editor is really worth its weight in gold. It is a total time saver for standard replies (template).
Also support is very good and the author is open to good suggestions. Love the font preview feature - I didn't even know it was supplied by you, as I have been using Stationery for a long time now.
This review is for a previous version of the add-on (0.7.8).
This user has other reviews of this add-on.