Now that I've been using Apple's new OS for a few weeks, I feel I can say something about it. I have a MacBook from 2010, so I upgraded from Snow Leopard. Before buying that PC I had been using Windows since Windows 3.1.
I was worried that the upgrade would result in a slower PC. That used to be the case with Windows. New Windows version meant you would either need to buy a new PC, or at least buy more RAM, or be patient with the PC. Having upgraded to Lion I'm happy to say the MacBook feels as fast as before.
On to the features of the new OS. I appreciate not having to restart all apps after restarting. The PC now does that for me. I also like the Mission Control, which gives an overview of all apps. Would be nice if the web browser windows didn't obscure each other. The Auto-save and version control make me feel safer when editing documents. Very good. Adding multi-touch to the laptops, Apple has done something very Appely. They have copied multi-touch from the iPad and iPhone onto the laptops. It's obvious and hence the right thing to do and it will be popular. Apple understands UI. If they didn't, then no important computer maker would. There may be other planets that aren't lucky enough to have Apple. Pity them.
Another thing they copied from the iPad and iPhone is the LaunchPad. I don't use it a lot, but putting it there was the right thing to do. Sooner or later I'm going to start using it instead of the almost as easily accessible program folder. It's more elegant, so lots of people are going to appreciate it.
The dashboard has become useful. I didn't use it much until Lion, because it felt unresponsive. The clock took several seconds to show the time. With Lion this problem is gone (although the first time after startup it takes as long as before). I often swipe it in just for the pleasure of swiping. That's the sign of a good user interface: you use it for pleasure!
I recommend OSX Lion upgrade. It's worth the money! I may come back with more in a few weeks. Like what I think about Xcode 4.