Bumpers: The bumpers on my Jetta were shortened, but retain fully functional bumper shocks. Simply remove the bumper shocks, use your Dremel tool to cut the welds on the back of the shock, then the shock itself comes free from the mounting bracket (with a little hammering of course). Simply drill new holes in the the bracket, weld in the new nuts, replace the shocks, placing them in whatever place you want, depending on the degree of reduction required, and weld 'em back togeather again. Be careful not to cut holes in the shocks with your Dremel, or to burn holes in the shocks with your welder. Of worth note is that I reduced the weight of my stock bumpers significantly by going to them with the old cutting torch. ;-)
For those of you with Rabbits with the big old heavy steel things, a good idea would be to pick up a set of Jetta bumpers. (quite similar to the European plastic bumper) Just attack the steel part of the bumper with the old cutting torch to reduce the weight, and make the bumper fit completely under the bumper cap.
a: maximum reduction w/o drilling new holes
b: original length
c: solid square tubing I'd been using for about 2 years
d: new shortened shock
Note: d could've been shortened about another 1/2 inch or so