I was having a problem with the reaer of my 05 OR squeaking and the general concensus on here was just deal. I was, but then I had to take my truck in for some other work and the dealership told me they would fix the leaf springs as well and I surely wasn't going to argue. I talked to the service manager and he said he has done a few and no recurrences. When I signed the paperwork it said "recall" next to the part. If anyone is having a similar problem it seems to be a free fix. Check it out.

I noticed this when I went last weekend "off road" on Devilhead Rd here in California. Since then, I haven't had a problem.

Any idea what they did to fix it?

yeah, there was a service bulletin out for this... just take it in and the dealer will squirt some grease in there as per the bulletin instr.
here's the link for bulletins: http://www.nissanhelp.com/Bulletins/Xterra/2005/1.htm

Actually, they replaced the whole leaf spring assembly. I talked to a few suspension people and they all indicated that grease was only a temporary fix. Supposedly the new springs will not squeak later.