Please note this is not a review and is not intended as a guide in any way shape or form...it's just some random notes on things I discovered whilst getting ready to install Mountain Lion and on starting to use it.
1. You should look at this page on How to Make a Bootable OS X 10.8 Mountain Lion USB Install Drive or look at this application (Lion Disk Maker) before you install Mountain Lion. I prefer to have a DVD of each OS to keep and so first tried Lion Disk Maker but it failed to function (note, it was a release candidate version of the app and appears to have had one update since I tried) so I ended up taking the more hands-on approach to burn a DVD. You'll need a dual layer (8Gb) DVD and be warned that the DVD is very slow to boot up once you create it...so you might want to consider the USB stick approach instead.
2. Screen Casts Online has created a superb free to view tutorial about Installing OS X Mountain Lion that I urge you to watch before hand
3. As always, Ars Technica has an incredibly detailed review of Mountain Lion. Interestingly, the author has also posted details on other ways you can view the review and support him and the site. The ePub version is a massive 117 pages long and worth every cent!
4. Roaring Apps have also updated their superb Application Compatibility Chart
5. If you really want to keep up-to-date with all your software, I recommend the superb AppFresh for checking if there are updates available to software. It seems to catch more updates than CNET's TechTracker, although both sometimes show inaccurate updates. AppFresh has just turned commercial it would seem and is for sale at $9.99 USD at the moment....I think that's a bit much, but the exchange rate makes it great at the moment.