WordPress is quickly becoming the standard software for the majority of blogs. This fact makes every major release of the software seem like a huge event, but the thing is that this time it is. WordPress 2.7 comes with a huge number of changes, a good chunk of them making some older plugins redundant. This will be a huge upgrade for all blog owners.
The following lists 20 of the biggest changes, but all together there have been over 400 changes to the program with version 2.7. (2.7.1 just came out recently).