Office 2010 is the typical Microsoft release.  If you already have the previous edition of their office suite, upgrading is purely a choice of preference.  If you are running older generations of Office it’s really a good idea.  If you are looking to purchase Office now..wait for 2010.  What does Office 2010 bring over 2007?  I am NOT an advanced Office user at all.  I have yet to find a Microsoft Office suite that’s truly easy to use for the Office neophyte…such as myself.  Ii have been playing with the beta and one thing it brings is usability.  The ribbon interface(which i also find much easier to use) carries over form 2007 BUT unlike 2007 ALL Office products now have the ribbon interface.  In 2007 Publisher and outlook did NOT have the full ribbon interface.  Microsoft has a tiered suport system based on the age of the product:

Support provided Mainstream Support phase Extended Support phase
Paid support (per-incident, per hour, and others) X X
Security update support X X
Non-security hotfix support X Requires extended hotfix agreement, purchased within 90 days of mainstream support ending.
No-charge incident support X
Warranty claims X
Design changes and feature requests X
Product-specific information that is available by using the online Microsoft Knowledge Base X X
Product-specific information that is available by using the Support site at Microsoft Help and Support to find answers to technical questions X X

Office 2007 will be in mainstream support until mid 2012.  After that the only updates available for Office are security updates…bugfixes, design issues, etc etc aren’t patched at all.  What are my recommendations for an Office purchase?  If you already have Office 2007 and it’s working fine for you stick with it.  By the time mainstream support ends for Office 2007 Office 15(whatever year that’s going to be) will either be released or close to being released.  If you don’t have any suite at all I would wait if at all possible for Office 2010 which has a tentative release date of June of this year.  If you have on older version of Office I would also wait for 2010.