What is the best way to prevent users seeing errors while an upgrade is in progress? The under construction plugin I'm using doesn't prevent this. Temp .htaccess redirect to construction page?

Thanks!

The best way is to use a redirection in the .htaccess file. A very good example of this is available in the 1.4.3 Development release with the "site_upgrade" plugin, but could be manually managed until then.

Download the development nightly and look at its zp-core/htaccess file. In the front of that file are some comments about the redirection. Just stick those (or the equivalent) into your current .htaccess file. Uncomment the redirection when you are upgrading.

All this will be handled by an admin utility button with the 1.4.3 release.