I’ve had a chance to work with the Outlook 2010 Technical Preview, and so far, I’ve been very impressed. The first difference you’ll see between 2010 and 2007 is that Microsoft added the Ribbon interface to 2010. The Ribbon interface has remained fairly controversial, with a lot of mixed opinions. I personally am a fan, it seems to be a lot more efficient.

Outlook 2010 has streamlined the new email screen, making it much easier to see which account you’re emailing from if you have multiple email accounts that you use. It also lets you quickly delete people from your autocomplete in the To and CC fields. That alone is worth the upgrade in my book.

Another huge change they’ve made with 2010, is a completely revamped print dialog. It shows you exactly what you’re going to get printed, and makes it much easier to change settings compared to what 2007 allowed you to do.

Those are some of the major mail related changes. For those of you who are wondering, some Outlook 2003/2007 plugins still work. OsaSync ran without any issues, however, I couldn’t get Xobni to display correctly. Hopefully there will be an update for Xobni soon.
I’ve found 2010 to be very stable, even with a multiple gigabyte PST file. The only times I’ve run into issues were with plugins that didn’t work with 2010.
Outlook 2010 is shaping up to be a must-upgrade product. Lets hope no major issues crop up between now and when they release it.