Pros:
1. Full screen apps are now a standard on Lion. For people who are not used to Mac OS, this may seam like not a feature. I didn't realize the difference it made until I started using it. Working on a 13" MacBook Pro (mid 2009) for a long time I had gotten used to working on a tiny screen. When I upgraded to Lion I couldn't believe how much of a difference it made. Now I, for the most part, always work in fullscreen mode on applications. Why? Firstly, it makes use of the whole entire screen and not just parts of it like before. Secondly, no more window management. Using a 4-finger gesture you can swipe between applications in full-screen mode. It's quite sleek.
2. Launchpad. Now there is a view on Lion that displays applications in an iOS like way. Now one can see all applications in a grid view across the entire screen. This makes it easier when trying to find an application in a hurly. Launchpad can be activated with a pinch gesture.
3. Mission Control. Mission Control allows one to see all windows in one area. Basically it is an updated version of Exposé. To note, the Exposé button on a Mac keyboard will launch Mission Control on Lion. What is different about Mission Control is that it now groups windows based on the window's application, which makes it easier to find the window you are looking for. Also Spaces is put on the top of Mission Control so you can easily create new desktops or delete desktops.
4. Spaces. Spaces was on Mac OS before but it was really hard to use. I gave up on it. Now Spaces has been updated and is a lot more easier to use. This is what I have been waiting for for a long time. Now, Spaces can easily be managed via Mission Control in an easy way.
5. Mail. Male has been update on Lion. It now has an iPad feel to it. It shows all your message headings in a narrow column on the left of the screen and then shows the actual messages in a wider column on right. If you have two or more messages linked to an original messages (replied messages), it will show all your messages in a discussion view where you can scroll up and down showing all the messages in a discussion.
If you have a hard time visualizing this than go to the mail app on your iOS device, it looks exactly like that.
Cons (more bugs than anything):
1. Gestures. There is a learning curve to the new gestures. One of the fist things was the scrolling. In Lion scrolling is done based on what you would do on iOS. Scroll up to move the page down, and scroll down to move true page up. It is not necessarily a "con" but is a nuisance at first. Once you get used to it, it is fine.
2. For some reason Safari gets hung up when quickly scrolling through webpages. It will stop responding for a moment and then usually it will catch up and start working again.
3. A lot of time the close button on tabs in safari will not show. In order to close a tab you have to click on a different tab and then click back onto the tab you were trying to close. Once you do that the close button will re-appear.
4. On rare occasions Safari will not allow you quit the application. This gets really annoying because it will stop the computer from shutting down and then you are stuck until you can quit Safari.
5. Rosetta stone is no longer on Mac OS. This means you can't run your old PowerPC applications.
These are just some of the pros and cons of Mac OS Lion. If you have any questions be sure to contact me.