My favorite Drupal trick for local theme development

.htaccess

# Find this line and insert the code below it (adapted to use your sitename/server).
# RewriteBase /

# Use files on the dev server instead of syncing them locally.
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^sites/sitename/(files/.*)$ http://dev.whatever.com/sites/sitename/$1 [L,QSA]

Thanks for the nod I definitely have used that since Sony.

Awesome, thx jacine :)

Only one thing, to get it with Git working without commiting this change:
git update-index --assume-unchanged .htaccess
is your friend, more infos:

http://gitready.com/intermediate/2009/02/18/temporarily-ignoring-files.html

Alternatively, you could:

drush dl stage_file_proxy && drush -y en stage_file_proxy

Then put this in your settings.php:

<?php
$conf['stage_file_proxy_origin'] = 'http://dev.whatever.com';

The advantage of the stage file proxy module is that it "...transfers each requested file just in time when it is requested" which is generally faster for local development than hotlinking to the production site, and also gives you the benefit of having the files to work with locally eg for imagecache manipulations when you request the original file.