After sailing today in pretty decent winds, the Super77 held the numbers on great! There are just a few places where the numbers are a little floppy, and that's where I kinda skimped on the glue. Dunno how long it'll last, but a can of that stuff is less than the cost of one new number, so I highly recommend it!
Edit: In case anyone is wondering just what I did, here was the procedure:
1) Peel number all the way off.
2) Lay out some paper towels. Put number upside-down on them, straighten as best you can, and put on a thick coat of Super77.
3) Wait 30-45 seconds.
4) Apply thin coat of Super77, and immediately apply number to sail.
5) Repeat with all crappy-looking numbers.
6) ???
7) Profit.