How much do you drive on the street, and how aggresively?
If it isn't driven on the street much, or if you drive fairly conservative, I'd go ahead and weld the rear. Offroad, you'll love having that locker up front in conjunction with a locked rear.
There are some people that have welded the front, since its only used offroad (typically) but personally I'd stay away from that unless you've got hydro assist. I've got a spool in the front of my truck (D60) and it is a pregnant dog to turn in 4wd. Hydro assist is definitely on my list.
If you run a welded rear, you're going to chew up your tires a bit more than normal, however if you drive faily conservatively, as mentioned above, you're keep that to a minimum.
