After long wait, Force.com IDE team finally released an update for Winter’12 release. To see what’s new and supported platforms, please go here : http://wiki.developerforce.com/index.php/Force.com_IDE_Release_Notes
If you are doing clean install or using older version of Eclipse before 3.6 (Helios), you can check the install/update instructions in this wiki page. Though I don’t like those mentioned in this wiki update guide, as it requires you to open “Force.com start page”, that is smart enough to crash the eclipse or would take ages to open on faster internet connections. If you are on Eclipse Helios, my preferred way to update in a simpler way is as follows :
1. Goto “help > check for updates” in eclipse menu :
2. Let eclipse search for updates, until it comes with a dialog like this. Select “Force.com IDE” and hit “Next” button, as shown below:
3. Hit “Next” on the next screen :
4 : Accept the license terms and finish as usual :)
5. Let eclipse download the updates, once done you will get a notification to restart Eclipse. Restart it and you are all set to use Winter’12 IDE.
After restart you will notice this classic popup asking for Force.com project upgrades.
I usually do a clean checkout of project again, as I work on very small and selective metadata required at point of time. Why selective metadata, checkout this blog post for more details : http://www.tgerm.com/2010/03/fast-save-refresh-force-ide-eclipse.html