Guess what, WordPress 2.3 Beta 1 came out last week and after doing some initial testing, Breadcrumb Navigation XT will work as it currently does except for archives by tags. Since the default theme still has some work to be done to support tags properly, I will defer programming in support for tags until Beta 2 or 3. Feel free to do some playing around with WordPress 2.3 Beta 1 and Breadcrumb Navigation XT 1.9.3. And, by chance, if you find a bug report it please.
Oh, yeah, by the way, WordPress 2.3 as of Beta 1 does not support tags in syndication feeds, only categories.
[end of transmission, stay tuned]