It looks like Thunderbird has come a long way in the last couple of years. I was able to install Lightning 1.9.1 and the Exchange 2007/2010 Calendar and Tasks Provider 1.8.5, and have access to my email and calendar.
I ran into some issues with the email address not matching the account name, and Thunderbird keeping some settings locked away in its memory somewhere even though I had changed them in the GUI (the account name kept the gmail.com value I had type, before correcting it to my work address). I also had to delete the account several times before finally figuring out that it was defaulting to GSSAPI authentication, even though I am not doing GSSAPI authentication.
The address book was a snap to configure. At first I thought I’d have to know the OU and Bind DN, but just putting in the ldap server name was sufficient to search for people.
Calendaring was also a snap. After installing the Exchange 2007/2010 Calendar and Tasks Provider add on I spent some time trying to figure out how to access the calendar and finally figured out there was a teeny tiny calendar and task icon in the top right corner. Clicking on them opens a Calendar and Task tab, and they appear to work quite nicely.
So, now I won’t be late for meetings, and I can edit work documents.