Ok, Lion was installed yesterday and I was, apparently, in good company because 1 million other Mac owners upgraded along with me.
Scrolling with a Track Pad or Scroll Wheel
Ok, using the scroll wheel on my wireless Mighty Mouse is taking a little bit of getting used to. In Lion, scrolling like like scrolling in iOS; you flick up to move the page down. Basically, we're talking about an inverted y-axis here. Fortunately, if you can't make the adjustment, of you're like me and I have to use a PC at the office, you can revert the scroll wheel functionality back to the way it was in Mac OS X Leopard and Snow Leopard in the Mouse control panel.
iChat Group Windows
Another application that I use all the time is iChat. I use iChat as my client for Jabber chats like Google Talk or Facebook. In Snow Leopard, I would have a chat window for each service. Now, in Lion, all my friends and buddies show up in a single unified window. When a new chat is started, a separate chat windows appears. If I have multiple chats going on at the same time, I can use iChat's preferences to define if all of the chats should be combined into a single chats window with tabs along the left of the window for each chat thread, or to appear in separate chat windows, as was the case in Snow Leopard.
I had the chance to test both modes out while chatting with two of my friends this evening. I like the consolidated buddies list, but I still prefer to keep the chat windows separate. I very fine tweak to iChat if I do say so myself.