Having switched to GNOME 3 via Linux Mint 12 lately, there are a few things I do to GNOME 3 routinely to make it fit me better. I'm collecting them here.

A lot of these tweaks are just gsettings items that aren't exposed in the UI anywhere. I show how to modify them with the CLI program gsettings, but it can also be done through dconf-editor from the dconf-tools package. gsettings and dconf replace the XML-based gconf, for no good reason other than to move away from XML, AFAICT.

Middle Mouse Button Emulation

My primary mouse at work doesn't have a middle mouse button, and I need it for Firefox (new tab, open in tab, close tab, ...). From http://who-t.blogspot.com/2011/04/gnome-30-middle-mouse-button-emulation.html:

You can also apparently do this through the gpointing-device-settings GUI, but for me it had no effect (the Timeout value did however...?).

Don't suspend on laptop lid closed

When I'm hooked up to a docking station and close my lid on AC power with an external display, the laptop should not go to sleep. (A bug if you ask me.)

Printers

The new Add Printers functionality in GNOME 3 never finds any printers for me, and AFAICT you can't add them manually. The old interface is still available, in the system-config-printer-gnome package.