Brion-
Another possibility is simply to 'blacklist' known problem browsers by printing a notice/link to better browsers on the edit page warning that they may have problems,
For the record, I would support blocking problematic browsers from editing entirely. If UTF-8 has enough advantages (and many people seem to think it does), then telling 2% of the userbase that their browser is outdated and corrupts pages when editing seems acceptable. Perhaps we can do it in a smart way and provide links to alternatives for each blacklisted browser (e.g. Netscape 4->Mozilla).
On the other hand, I would not support any solution that still leads to corrupted pages.
Regards,
Erik