Thanks for the feedback guys! I'm glad you like the idea.
I'm not trying to be bulletproof here, just trying to be better than the bike on either side of me. I am fully aware that nothing will ever stop a determined thief, but the average thief won't be showing up with a car battery and power inverter or portable generator (in the middle of a college campus, no less) to run his angle grinder... so I'm not too concerned about that.
Plus, even if he grinds off my U-lock he'll still have to defeat my cable lock and for that, an angle grinder is not so handy (unless he brought his workbench/vice with him, too).
By the way - if you wanted to carry two (since most places will only sell you 1-ft increments), it would be handy when you lock up to something small - the additional one will act as more of a space filler and make it difficult to attempt to pry/wedge on the lock.
My next idea (if I couldn't find the right size chain) was to use flat-stock steel (let's say, 1-1/4" x 1/8" or 3/16"). Drill the right sized holes in the right places and round off the corners with a grinder (so they don't cut holes in your bag or rip your legs off when you walk by). I think the chain is more imposing and difficult to destroy, plus it takes up more space. The flat-stock would be (most likely) a lot less weight, though.