First Impressions of Lion
The changes to the gestures in OS X are dramatically different. I can deal with the change to scrolling direction on a page (up is down, down is up) - that's really not that big of a deal. After less than a week I've completely adjusted to it. You can switch it in settings if you like, however you are better off just adjusting to it if you are exclusively a Mac user since it matches up with how actual touch screens like the iPad work. Apple wouldn't be making a change like this just for consistency, I believe it's to prepare Mac users for the future when a hybrid device that is a merger of iPad and Mac is released.
What is a big deal is that the default behavior for going back in a browser (three-finger swipe left) is changed, now it's two fingers and only works on Safari (not Chrome). I'm hoping I can get this to work in Chrome because for now I'm back to using Safari. I understand why Apple did it but it's made using my Mac feel very awkward for now.
Full Screen Mode
I like it - though having another button for doing this seems excessive. I don't know of anyone that uses the Zoom button (green + in the caption area). We've seen by the gestures that Apple is willing to completely change behaviors, why not this one? I do like that it also hides the menu bar at the top, which is great for letting you focus on content. Move the cursor to the top of the screen and the menu bar "un-hides".
What is a little odd is that moving the cursor to the bottom of the screen while in Full Screen Mode does not bring up the Dock Bar, so you can't easily launch another application while in that mode. This makes sense though since the application you are currently running is taking over the entire screen. Instead you can hit the old Exposé key (or the Mission Control gesture) and launch another application from there.
I haven't upgraded my dual-display Mac Pro to Lion yet (it's actually still on Leopard), but I'm interested to see how Full Screen Mode works in that environment.
Like many of the user interface elements in Lion, the scroll bars are now very muted in appearance. The big change is that by default they are set to auto-hide when not actually scrolling. While that behavior is brilliant on an iPhone because of the severely limited screen real-estate, that's not really the case on a full size display on a Mac. Why not? The scroll bar not only provides you with a general scrolling mechanism but it also gives you immediate feedback on how long your document is. Without it there you need to touch the scroll gesture just to see it. Fortunately you can change that in System Preferences to always show them, which is what I have done.
Love it and hate it at the same time. I use Spaces heavily and I don't like that I've lost my nice little grid and that it's now a single line across the top portion of the screen. It's lost keyboard navigation (arrows) between the "desktops" while in zoomed out mode, though I can assign Control-# keys for each of the Desktops. I like that the gestures for Mission Control allow me to simply swipe side to side (3 fingers) to move between them. This should expose it to more people that Spaces, which was really more for the techies out there.
The changes are not too bad on a modern Track Pad equipped MacBook Pro where the Track Pad is very close to the typing position. If you are an external mouse user then it's a much more difficult proposition.
This is just useless to me as a power user. I assume it's there to help new switchers that are coming because they love their iPad or iPhone so much. I can see that it would be much easier to guide a new user through finding and launching an application rather than having them scroll through the Finder's Application folder, however I'll just stick to launching my applications from LaunchBar.
Really like the new Mail overhaul. I use Mail extensively and this is just great. I like the appearance, the way threads of messages are kept together (ala Gmail), the drag metaphor (click and hold a second, then a message is draggable). Looks fantastic in full screen mode.
Calendar and Address Book
This is a rather large mistake by Apple. They are going for a "real world" object look and compromising functionality by doing so. The Address Book in particular is far less usable. Hoping they don't try this little "making it look like it's a real world object" with Mail (look like a piece of paper pulled out of an envelope), iTunes (look like an old record store with a demo turntable), iMovie (an old film splicing machine), etc. This is not enhancing usability at all.
I've been getting exceptions thrown in Safari pretty regularly. Since I upgraded from Snow Leopard I had quite a few utilities installed and I think one or more of them could be causing issues. Make sure you check the applications you normally run all the time to see if there are Lion specific updates available.
Other Little Things
If my MacBook Pro drops into sleep mode the trackpad no longer wakes it up; I have to hit a key on the keyboard. One of the utilities I've come to depend on—Growl—is not currently supported and I find myself lost without it. Performance is very good overall, and Snow Leopard was no slouch. Safari is considerably faster and the new Back / Forward animations look very slick.
With Snow Leopard Apple brought OS X fully into the 64 bit world, preparing the operating system for the next generation of software to come. With Lion Apple is now doing the same thing with users, preparing us all slowly for a world that is driven by portable devices, not personal computers.
It's a lot easier for Apple to get the average person to buy an iPad and use that for Email, web browsing and some basic applications. People don't consider that "switching" - it's an entirely new paradigm to them. Given that, I think we will continue to see the innovation at the user level happen on the iOS front and that will drive direction for the foreseeable future.
You may read what I have written and think I'm not happy with Lion. That would be incorrect. I really like Lion and the problems I'm pointing out are because of frustrations I have with something I spend so much of my day using.