If you're confused, I'd highly recommend Practical Cryptography by Niels Furguson and Bruce Schneier: http://www.schneier.com/book-practical.html
It will give you much better advice than the internet will.
Why do we care about HTTP Digest? It provides a standard technique to avoid sending clear passwords from client to server. This is particularly handy when the client server communication isn’t encrypted (a poor man’s SSL if you will), but sounds like a good idea in general.
In principle you could create a variant of HTTP Digest using bcrypt instead of MD5 however you’d break browser and rss reader compatibility and AFAIK there are currently no javascript bcrypt implementations.
Hence I’m guessing that web apps storing bcrypt hashed passwords are forced to send clear-ish passwords from client to server and therefore must rely on the presence of an ssl/https connection.
Obviously ssl should be used whenever possible, but I wonder to what extent sending clear passwords doesn’t create other forms of vulnerability?