Got mine done this weekend. Replaced all 4 with Moog parts - which are substantially beefier than stock, are greaseable, and have a lifetime warranty (for whatever that's worth). LH side took me 8 hours (ugh) and a lot of cursing, until I learned the tricks all of which are well documented here:
http://www.explorerforum.com/forums/showthread.php?t=188225
After that, the RH side took me only 2 hours. Note: I did upper joints too, so the LH side is a bit of a pain fighting the UCA bushing/alignment bolts.
Follow the instructions verbatim, applying liberal amounts of whacking where necessary. 2 words of caution: wear hearing/eye protection, and NEVER hit the spindle (cast) with a metal hammer. Always hit the control arms which are stamped or forged. A 3-4 lb sledge, a meaty pry bar, a floor jack, and a rented ball-joint-press are essential.
I still have a bit of a rattle/clunk over bumps, even after replacing the sway bar bushings... so I'm still on the hunt for that source. But overall, performance is way improved. Pretty much all the ball joints had enough slop in them that I could make them "clunk" by hand - the RH lower was completely dried and rusted out and what was causing the grinding noise.
Amazon has the parts cheap - roughly the same or a bit cheaper than RockAuto... and I have Amazon Prime, so shipping was free and FAST. Rock is really gouging lately on shipping... they just ripped me $15 to ship 2 lousy $3 axle hub nuts via standard shipping, and if your order comes from different warehouses the S&H price soars.