Autodesk has released the new Web Updates, Service Packs, or Builds (wish they would stick with a name) for the Revit 2009 platform.
What is new for this release is that you are now able to install just the "update" to an existing installation.
Here are the links of note.
Revit Architecture 2009 downloads
Revit Structure 2009 downloads
Revit MEP 2009 dowloads
There is of course a very LONG list of fixes / improvements that you can find from the links above.
For subscription customers, you can now download the 64-bit version of Revit. I used the beta of Revit Architecture 64-bit on a couple different Dell workstations with either 4GB or 16GB of RAM running XP 64-bit and saw noticeable stability and performance improvements.
You can download the 64-bit versions of Revit from the Autodesk Subscription site. On the left side of the screen you will see "Product Downloads". Click on that link and you will then be able to download the 64-bit versions from the list. Keep in mind that you need to be running a 64-bit operating system in order to use these versions of Revit.