Nikon today replaced the SB-900 with the SB-910. The primary change? Instead of shutting down when thermally challenged, the new version will slow down instead. Other changes include replacing the Zoom button with a Menu button, and the addition of two hard plastic fllters instead of gel. The plastic casing has been ever so slightly reshaped, but I don't see this as as a meaningful change--the new flash is still as big and bulky as its predecessor. Nikon also changed the LCD, which they describe as an improvement, though in early press photos it seems less contrasty (perhaps due to the use of backlighting).
Despite those minor changes, Nikon's press release used more than a dozen over-the-top adjectives ("revolutionary", "exceptional", and even "enhanced"). For what's essentially a minor point release update, the press release instead gushes like it was boilerplated out of the SB-900 release. Nikon could have simply written: "In response to user demand, we've made three small changes to create an SB-910 that should provide a better flash experience for everyone." Then outline the changes. Instead, the changes are buried in the details that are the same for the SB-910 as they are for the SB-900, leaving it to Web sites like this one to try to ferret out what changed.
The button change is going to please most, as the flash is a little quicker and straight forward to set up now. The filter change is welcome, as gels have a habit of getting unusable quickly. It's the thermal protection change that most will be looking at the closest, though. Like the SB-900, you can turn it off (at your own risk). But "slowing down" is not going to prove satisfactory to the photographer that's pressing their Speedlight to the max, I think. In an absolute sense, slowing down is better than shutting down. But it still likely means you'll miss photos. It's a shame Nikon didn't use their own patent for head cooling techniques, which would be a more welcome approach.