Linking to Rob Relyea again, this time he talks about  "Using Ricciolo PaperBoy 0.2 (WPF RSS Reader)".

With the IE7 RSS platform writing an RSS reader has got a lot easier.  Rob mentions that he typically uses IE7 to read his feeds - this is one thing I don't understand.  My OPML file has about 200 blog entries, most of which update maybe twice per month.  IE7 is next to useless reading these feeds because it doesn't aggregate news.  This same fault applies to Ricciolo Paperboy.  A news reader without aggregation to me is just like browsing my favorites but without the HTML formatting.

There is RikReader - http://11011.net/software/rikreader - which is also written in WPF, uses the IE7 feed engine and supports aggregation.  It's not too bad too, and comes complete with its own HTML to flow-document converter.  Like Paperboy, it's a little unstable with some feeds.

After using Google Reader for the past six months, I need to add hosted reading state to the list of requirements.  That means that I want a central server to know what I've read and what I haven't.  I also want to share items and flag items of interest.  Also, like with Google Reader, I want to be able to read these feeds on my cell phone.  So here's my must-have / nice-have list:

• Good reading experience - i.e. better than Google Reader's HTML effort.
• Aggregation (river of news) - preferably tagged, not hierarchical.
• Hosted reading state - ability to share reading state across machines and devices (as in Google Reader).
• Easy to install - Click Once or XBAP. 
• Blog writing integration - e.g integrate to Live Writer or similar.
• Comment support - ability to show comments and subscribe to comment feeds (if they exist).
• Browse support - ability to view Memes and browse blog entries and trackbacks graphically (like Times Reader).
• Mobile support - integrating reader state (so I can monitor what feeds are new)
• Podcast/ Vidcast support - enclosure support.  IE7 kind of has this already, but the enclosures go to the temporary Internet directory.  A news reader is a good chance to fix this - just copy those enclosures to a perconfigured directory and do some transcoding in the background.
• Offline reading - something that Google Reader doesn't do.

So, all this could be added to Paperboy - and it should be fairly easy to do (apart from the hosting, but even that could be made generic with some sort of polled external internet based file).   The only thing that stops me delving into CodePlex is the fact that I'm convinced Microsoft has a product waiting in the wings that will compete with Google Reader.  The Microsoft Max team did some of this already and the Live.com home page is very much based on RSS.  The (Times) Reader SDK must have the capability to render your own personalized newspaper  - based on your feed database.  Live Writer has quite a following, although this is a WinForms app - I don't think it would take much to integrate this into the mix.

So is the market that Google Reader holds worth going for?  From a purely financial perspective probably not.  For secondary effects, like winning the minds of influentials and the Web 2 community it has more merit.  It might be essential for MS that somebody like Robert Scoble uses Microsoft Technology over Adobe's or Google's.