07 is far more intuitive that was the first thing you will notice. It makes sense where things are located.
If you have used 03 you might be a little frustrated finding out where anything is located.
File sizes are greatly reduced, more functionality, Very aesthetically pleasing.
Outlook, I really don’t know my personal experience is having just outlook 07 running on a work machine which i remote to for the sole use of the calendaring. I felt the exchange setup was bullshit, but thats no different than 03
Word has somethings that I initially didn’t agree with some of the default spacings I just didn’t agree with but I’m rather picky about 1.5 spacing and 1 line spacing, so this may not bother you
Excel, simply improved again file size of xlsx was greatly reduced, and there is a good deal of added functionality that I really haven’t experienced with. It runs much faster too, calculations are cut in half (very noticeable in large spreadsheets)
Powerpoint, some slight incompatibilities with 03’ but generally just how it formats the spacings.
Groove 2007 I’ve heard is just amazing, I don’t have much experience with it though.
Infopath, One note, and Access I just don’t use.
Frontpage was omitted for obvious reasons