The interface is very iPhone-ish--looks great. For the "Now Playing" mode, I would suggest a volume control and current playing time (or graphical slider, like in iTunes and the iPod). These two additions would make the mode a full-featured iTunes remote.

Certain CSS calls, I understand, will make Safari hide the menubar. This would open up a bit more screen real estate. See here: http://www.joehewitt.com/blog/introducing_iui.php

Like the previous poster, I have a large library (~20,000 tracks), and it is very slow to browser in RB on the iPhone. While disappointing, this is certainly understandable, though. Most people, probably, do not have this problem.

Anyway, thanks for a neat and very useful application.