This evening I've tryed to play a bit with Doppler Mobile, all exciting to have found the mobile RSS Reader I need, but actually I'm a bit disappointed. 
Doppler Mobile is too much a beta, it's really a promising product but it has also lots of problems.
I've installed it on my Windows Mobile Smartphone with success, then I've tryed to add a feed (in my test I've added the main feed of ASP.NET Weblogs, located at http://weblogs.asp.net/MainFeed.aspx. The feed was correctly recognized (the application on the main page of the subscribed feeds shows the feed title and the number of unreaded post) but when I've tryed to read the posts, the application had an unexpected crash. Every action that I was trying to do after adding a feed, caused a crash on the application. 
The error reported was:
DopplerMobile.exe ArgumentException in Microsoft.AGL.Common.MISC.Handler()
in System.Drawing.Icon._InitFromMemoryStream()
........
(too long to be reported here)
and it seems to be an error on a resource (an icon?) created on the main form of DopplerMobile.
What is curious is that, when adding a feed, Doppler creates a folder (in my case \Storage Card\Application Data\Doppler) with these files:
35DF3780.fbz 19,5 Kb
35DF3780.ico 0 kb
Settings.dms
(the number are random generated and are relatives to the feeds cache).
If you remove the .ico files (empty file) and then re-launch Doppler Mobile, the application works, otherwise it has always a crash.
Why this?
Second, I've discovered that if you add a feed and then immediately exit the application (without reading feeds), Doppler seems to saves every settings correctly and the crash is avoided.
The second noisy problem is that when I read a post on my Smartphone (by selecting the post via the list under the selected feed) the text area that appears you (with the entire post content) start blinking (:C) and I can't scroll the entire text. I can read only the text that feets on my display, I can't scroll....
I've signalled these bugs to the Doppler staff and I hope on a response (and on a solution).