I've been using Office 2010 Beta for a couple of months and haven't found any problems. The programs launch really fast - the biggest improvement I've seen over 2007 or any previous version. I feel like I save lots of time when Word docs open fast and save fast...not sure if it adds up to much time but it is a noticeable difference!
You can use 2010 Beta free until Halloween if you'd like to play with it.
I've heard there are no upgrades from prior versions and everyone that wants 2010 will need to buy a full version. I would say skip 2007 and go straight to 2010 but I believe I saw that if you buy 2007 now you can get 2010 for free when it launches.
This is a good site for info on Office from Office Watch:
http://news.office-watch.com/?
Here is their 2010 Office pricing info:
http://news.office-watch.com/t/n.asp...1360&zoneid=10