With Microsoft Reader for Pocket PC you get:

• Remarkable content support and unmatched portability: Enjoy thousands of Owner Exclusive eBooks on Pocket PC — and take your eReading library with you wherever you go. With Microsoft Reader for Pocket PC you can easily copy books from your desktop/laptop/Tablet PC to your Pocket PC and continue reading wherever you are!
• Great on-screen readability: ClearType® display technology that makes text on screen crisper and easier to read than ever before. The adjustable font size setting makes it easy to customize your reading experience.
• Dynamic reading: features include highlighting, bookmarking, note taking, and drawing. Plus, you can view your annotations and rename or erase any of them at any time.

Update Description:
v2.41:
- This update addresses activation problems experienced by the users of some Phone Edition devices.

v2.4:
- It is a bug fix release primarily intended for users of devices running Windows Mobile 2003 and Windows Mobile 2003, Second Edition.

SOURCE

http://www.microsoft.com/reader/info/ppc.asp

Reviews:

***** [Apr 4, 2007] by Techguy using T-Mobile MDA
This software has a perfect dictionary reader in it. It also has a way to change the font size very easily.

***** [Jan 17, 2005] by J. Chronowski using Compaq Ipaq 3955
Finally got Reader to play my Audible.com files. Best thing since sliced bread to delete the Audible Reader and gain about 10 megs back. I just wish that MS Reader would also support pdf books. Fat chance. I know. I am refering to purchased .lit, .aa, .pdf content not free content.

***** [Jul 28, 2004] by Dutch Zellers using iPaq 2210
Have you tried using Convert LIT (http://www.convertlit.com/) to convert your eBook to html? I've done it with a number of .LIT files and am using uBook as you suggest. Give it try!

** [Jul 21, 2004] by Matt S. using Dell Axim x5
Why does Micosoft continue to put so little effort into this reader? With all their billions and programing ability, why does this program remain the most basic reader out there? No landscape mode unless you have WM2003SE??? Still no auto-scroll function? How is it that freeware readers developed by individuals kick this thing's butt? If µBook would only support .lit files, I'd remove this thing from my pocketpc ASAP.