There are several subtle changes along with the 'biggies' in Adobe Lightroom 3. While converting and checking out all the conversions and functionality these new and old important items came up:
Under the File Handling Tab of the Preferences option from the Edit Pull Down from the top bar of Lightroom
1. Varying the setting for 'Camera RAW Cache Settings' may improve your multi-tasking speed a lot. Lightroom is built to allow editing and sorting to continue while various output operation are going on and how much space for the RAW previews is allotted will make a huge difference when switching back and forth between various images. Using a second display for previews or compares can be greatly augmented with this parameter depending on hardware and software obviously. The Red circled default Max setting of 1GB is shown and can be increased or decreased. This was first available in LR2.x.
2. In the same Screen Shot Illustration underlined in Red is the File Name Generation options. There is new added functionality throughout Lightroom 3 in the entire Metadata/file Handling/sorting Database and this is one place that a series of important tweaks can be made. Note the options in the Pull Down Menu regarding Space Handling in File names. Important as it can alter your file name unexpectedly!
NOTE: The big Purge Cache button! Very handy to free up space when working with a large number of images and Virtual Copies.
There is also a change in Keyword Entry with a delimiter option for Commas or Spaces under the Interface Tab of the Preferences option from the Edit Pull Down from the top bar of Lightroom.
Circled in Red and arrowed is the important option.
NOTE: The option for Auto-complete Text in Keyword Tags field will aid in adding to or sorting similar Keyword sets if enabled as it is by default!
Watch for potential updates on these topics!