I think that's a very good proposition. Using both outlook 2007 and TBird 3.1.8 with the lightning calendar extension, I can say IMHO that the latter combination is better than Outlook in some areas, particularly calendar and task sharing with multiple computers via something like icalx.com.
On a different note, it's quite interesting to see that MS seems to be employing some dubious tactics with regard to the Home & Student version of Office 2010. That version is very attractive to home users because it's pretty cheap and can be installed on three computers.
However, what MS doesn't tell you is that it contains a TRIAL version of Outlook. Of course people think "Oh goody! I can use Outlook." Then 60 days later, Poof! it needs to be purchased to continue using it, and if you have a version of Outlook prior to 2007, it can't use the pst file created by 2010!