I did something like you did when I bought LR-3, figured having the disc would be a good idea. But then not long after that LR-3.2 was released and it was the entire program that was replaced, not just a patch so I ended up downloading it and then replacing my LR-3 with it. Then came LR-3.5 and it was the same, a total new download instead of a patch. Same thing with LR-4, the new LR-4.1 and LR-4.2 are complete downloads. So basically the only time you'll ever use that disc is the very first time you load it. And chances are you've already got the program running on your computer under the 30 day free trial, so you might not even use it for that.
On the positive side, Adobe forces you to have an account with them as a part of the product registration. I was a little annoyed by this but now love it and am grateful they forced users to have one. They will store all your serial numbers for you so that when you're switching computers or you're loading LR on to your laptop (you can legally run LR and PS on 2 computers at once, btw) you can simply go to their website and find all your serial numbers. And if you're like most of us and do upgrades from LR-3 to LR-4, you have to put in the serial numbers for both programs, so having all the serial numbers in one place is a very handy thing.
So in a long and drawn out way, it's nice having the disc but you'll quickly find it is just another thing on your shelf gathering dust.