1. Previously, when you're viewing a picture in Preview, you could delete that file by hitting Command-delete. Now you cannot do that. You may attempt to add a delete icon by customizing the toolbar but you'll notice a delete option is not available.
2. If you are using a magic mouse, you cannot disable the control-left click to simulate a right click button. So, if you're in a program like VMWare Fusion running XP and would like to highlight several non-consecutive items with your mouse, you cannot hold the control button and select each item with the mouse.
There appears to be a workaround for VMWare in the settings. You can unselect an option to use Mac shortcuts in your VMWare but that removes all shortcuts like the Command-C for cut and Command-V for paste. I used to like keeping those so it's consistent for both my mac and pc sides.
3. I used to be able to press my middle button to get to the dashboard. Now I have to press my F4 button or use a two finger swipe to get to a dashboard screen.
4. When you buy your computer with Lion already installed, there's a hidden partition on the hard drive that contains the installation files in case you wish to reinstall. However, what if you want to remove that hard drive and replace it with an SSD? How do you reinstall the OS? The computer does not come with a DVD with Lion so that's not the way to do it. The solution is to download it from the internet using a menu built into the bootstrap. I might not always have internet available so I don't like this option. So, I ended up ordering a USB device that contains an installable Lion OS. The instructions say "Hold down Command-R during startup to boot into the Recovery HD, or hold down the Option key during startup and select Recovery HD" Neither of those options show the USB drive so I was forced to install using the Internet option. I currently have business class internet service at 22 - 50 mbps so it didn't take too long but what about those poor souls on dial-up or standard <3 mbps connections? I'd still like to figure out how to use that USB drive and I'm sure there's a way but they don't make it easy.
Imagine if you bought Lion using the App Store. Do you need to install your Snow Leopard first and then download lion again every time you reinstall.
Most people may not need to reinstall that often but I do. I like to test software that is in beta and could potentially make my computer unstable.
5. The old Activity Monitor used to display all processors and a graph displaying their percent used. The new one doesn't have that feature. You get a chart of all the processors combined that moves with time (It's labeled as CPU Usage but should be labeled as CPU History). You can get the true CPU Usage display by using the menu Window -> CPU Usage or Command - 3 but that's in a separate window. When you minimize the Activity Monitor, it no longer shows your CPU Usage in the icon and you do not have the option to minimize the CPU Usage window that pops up with the Command -3.
This is important for some of us that use multiple OS's at the same time. It's not unusual for me to have three VMWare operating systems running at the same time. I need to know if a slow-down in one of the windows is caused by a CPU overload so I like to monitor that carefully.
6. I used to enjoy watching new trailers with Front Row. That application is either missing or in a location that is not easy to find. I have been unsuccessful in finding it on my standard Lion installation.
7. Repeat keys have been disabled by default. That means if you're in a text box and you hold down some of the keys, it will not repeat. Try holding down the "n" key. Instead of putting several n's on the screen, it pops up with a menu that allows you to select foreign versions of this letter like the ñ or ń. This can be changed in preferences but why would they change a basic behavior like this and make you hunt down a way to change it back? This is the same with the mouse scrolling. It's completely backwards from any operating system you've ever encountered. Usually when you scroll down, the text moves up. Now, with Lion, the default is when you scroll down, the text moves down. Additionally, scrollbars are missing until you move your mouse to where the scrollbar would normally be or begin scrolling. Very annoying so these need to be changed in preferences to be "normal" again.
8. Youtube is jerky when viewed with Firefox. You'd think this has to be a Firefox and Adobe issue but it isn't. You can install the same versions of Firefox and Flash on a Snow Leopard system and it works fine. Surprisingly, you can watch the same video posted somewhere else and it works fine. Also, if you watch it in full screen it works fine too.
9. Lion has a new Launch Pad feature. No complaints with that but it doesn't seem necessary. Why do I need this when I can just click on the Applications icon in my dock to list all my applications instead of just some of them listed in the Launch Pad (unless I scroll horizontally to see the rest)?
10. I'm locked out of my own library. Several third party applications have text or XML files that you can edit to modify their behavior. You cannot find your library files anywhere. There is a workaround for this one though. Getting back Library access is achievable via a brief use of the command-line, just launch Terminal and copy and paste the following inside, then press return:
chflags nohidden ~/Library/