I am also underwhelmed by the built-in reader, mainly for having no offline mode.

I think one potential port possibility for the N900 is an open source iphone offline reader that interfaces with google reader, called GRIS.

http://code.google.com/p/gris/

It appears to be an Objective-C GUI on top of Python 2.5 code. I don't know what the effort is to port, but it'll be the first thing I look to learn as my time frees up, assuming nobody else gets there and does a bang up job first.