Clone into ~/config as 'shared'. This contains your shared system config.
Create ~/config/local/bashrc and a new local repository in that directory. This contains your custom config for this system.
Quit textmate.
Symbolically link textmate's custom bundles directory:
$ ln -s ~/config/shared/tm_bundles ~/Library/Application\ Support/TextMate/Bundles
(If you have bundles already in that directory, you should move the ones you want over to the tm_bundles directory, and remove the Bundles directory.)
Reload bundles:
$ Bundles > Bundle Editor > Reload Bundles, in TextMate
To install more bundles, clone them into the tm_bundles directory, e.g.
$ cd ~/bin/tm_bundles
$ git clone git://github.com/rspec/rspec-tmbundle.git RSpec.tmbundle
Symbolically link textmate's custom plugins directory:
$ ln -s ~/config/shared/tm_plugins ~/Library/Application\ Support/TextMate/PlugIns
(If you have plugins already in that directory, you should move the ones you want over to the tm_plugins directory, and remove the PlugIns directory.)
To install more plugins, move the .tmplugin file (directory) into the tm_plugins directory, e.g.