CRM Mobile Express Bug Tracker
There seems to be a few bugs with the first release of CRM Mobile Express. Currently, GotDotNet.com is maintaining a list of bugs that users have discovered. As the bugs are fixed they will posting hotfixes on this website for you to download and install. If you ran into a potential bug that is not listed you can report the bug on this website as well.
For those of you that upgraded from CRM 1.2 to CRM 3.0 bug #4 may be of some interest to you. When you upgrade to 3.0 setup renames custom attributes and adds the letters CF to the name of the attribute. With the way the mobile express client handles capital letters this causes issues in the mobile client if any of your entities are actively using one of these fields. Bug #4 addresses that issue.
I recommend checking this site every couple of weeks to see if any new bugs or hotfixes have been posted.
GotDotNet Bug Tracker Website:
http://www.gotdotnet.com/codegallery/bugtracker/home.aspx?id=8e65fc13-4073-406c-879c-442faf78f2c8