The newest Mac OS, Mac OS X 10.7 Lion, was released last week. See [John Siracusa's review](http://arstechnica.com/apple/reviews/2011/07/mac-os-x-10-7.ars) for a extremely detailed look at the new features in Lion. AstroBetter posted some [thoughts on Mac OS X 10.7 Lion](http://www.astrobetter.com/os-x-lion-install/) along with a comment thread from users about how it has affected specific astronomy packages.
My thoughts from using Lion for a few days on my home computer (I haven't upgraded work computers yet):
1. IDL seems to work fine, though I haven't done much on my home computer besides a few sanity tests.
2. Lion is the first Mac OS X update I have thought felt slower than its predecessor. I think it is mostly due to the new [window creation animation](http://arstechnica.com/apple/reviews/2011/07/mac-os-x-10-7.ars/4#animation). The extremely useful Secrets website [says](http://secrets.blacktree.com/edit?id=178761) that the following should turn off the animation: "`defaults write NSGlobalDomain NSAutomaticWindowAnimationsEnabled -bool NO`".
3. Spaces have been changed a bit to work with the new Mission Control feature. I had a 2 x 3 grid of spaces previously, but Lion only supports a 1-dimensional array of spaces, so now I have a single row of six spaces. This is what I'm missing the most so far, since my 2-dimensional mental model of the purposes of the spaces allowed quick switching between tasks.
4. [Scrolling](http://arstechnica.com/apple/reviews/2011/07/mac-os-x-10-7.ars/3#scroll-bar) is, by default, backwards from the current direction, but there is a preference value to change it back to the Snow Leopard way. I suppose if I had a Magic Trackpad I would give the new way a try, but I use a regular mouse with a scroll wheel, so I stuck to the old way.
5. Most people are reporting an easy installation from the Mac App Store, but I had some difficulty. After Lion was downloaded, my Mac rebooted and the installer hung. It reported that it had 33 minutes to go for several hours. I tried again and it appeared to hang again, but I left it going all day as I was at work. When I come back, it had installed. Not sure how long it took, but it was definitely way longer than 33 minutes.
6. Rosetta support is gone, luckily all my applications are native now.
7. The UI is generally more muted and fading into the background, which I really like. On the other hand, iCal and Address Book got the [skeuomorphic](http://en.wikipedia.org/wiki/Skeuomorphic) treatment, which I really don't like.
8. For a few months, the new version of XCode cost $5. The new Lion version is free again.