I strongly recommend that Windows users refrain from updating to 1.4. A few issues that have been discovered:

 

If needed you can still download 1.3.1.If 1.4 provides support for your camera that is not found in 1.3.1 you could use the standalone DNG converter to convert them to DNG and then import.If you want to convert to greyscale with control over color noise then use the method demonstrated by Martin Evening.

Although some issues do affect the Mac version as well, the improvements in printer support may outweigh the time stamp on export and Modification Date issues.  There is not a similar significant gain for Windows users to make the upgrade compelling at this time. If you are a Mac user who does not need the latest camera support nor improved printer support on Leopard then you may want to pass on this update as well.

 

There is a great run down of issues and solutions over at LightroomForums.