GNOME3 has been around for quite a while and one thing which is hard to live with is its default ALT+Tab implementation. No, getting used to it is not a problem. The problem is that default was chosen wrongly. Regardless of time you spent using it, the change back is inevitable.
Let's go through in-depth analysis.
- The ALT+Tab logic switches around groups of windows. The windows are grouped based on application. It may simplify work when user commonly switches to different application. But why should we assume this? What about switching between two terminals, two PDF files, or two browser windows?
- The ALT+[key above Tab] logic switches around windows of the same application. It may simplify work when user commonly switches to windows of the same application. This logic "traps" user in the windows group. Is another window of the same application the most common one to switch to? What about checking page in the browser and switching back to a terminal window?
The most common use case of switching seems to be go back to the previous window. It has nothing to do with application group providing the window. And none of the option above satisfies this without occasionally using two key combinations. Moreover, it forces user to forget everything and think whether the previous window belonged to the same or different application. It's brain consuming.
GNOME3 (as it is in Fedora 16) has "Advanced Settings" application which is provided by gnome-tweak-tool package. It accesses to various extension. One of them is called "AlternateTab Extension"  - it is provided by gnome-shell-extension-alternate-tab package.
yum install -y gnome-tweak-tool gnome-shell-extension-alternate-tab
The "AlternateTab Extension" brings back the classic ALT+Tab with two options (options can be managed through a browser on the web site ):
- all_thumbnails to switch between all windows using thumbnails of all workspaces;
- workspace_icons to switch between all windows using icons in current workspace only.
The 2nd option is truly classic. Beside satisfying your past habits, it also provides isolation between workspaces. This is probably what majority tries to achieve by "splitting work into spaces".