Nikon has put a number of enhancements and bug fixes in this release so you will want to visit the download page. A couple caught my eye. First, they have increased the minimum shutter speed in Auto ISO from 1/250 to 1/4000. They have also made some AF improvements and what looks like a number of menu changes. If you use the MB-D10 battery grip with your D300 (I do), there is a fix for battery type information. Some GPPS fixes.
Users of the WT-4a Wireless Transmitter should be happy. Nikon had previously released a firmware upgrade for the WT-4 that was incompatible with the D300 1.03 firmware. V1.10 fixes that problem.
If you have a D300, this looks like a firmware upgrade you are going to want. I have already upgraded my camera though I have not gone out to shooting yet. Hopefully this weekend.