One of my favorite things about RoundCube is that is provides a "write" and a "read" dsn - I actually use this with MySQL as I replicate my databases across multiple machines from one primary server.
I wish more web applications did this! I've manually implemented it in Wordpress, though there are a few glitches and its more complicated than it needs to be.
Another thing I like about RoundCube is the user interface. Big surprise there, huh? Its simple, appealing, and very user friendly.