Replaced the front bumper cover on my '07 Focus. (Took a low speed trailer hitch in 2010, it's had a gaping hole ever since.) Since I had no idea what I was doing, I took my time, was careful not to break anything, etc., it took me 6 hours, but I only lost one screw. I could see where somebody who knew what they were doing could do it quick, though.
(While I had it apart, I also polished my headlights, touched up a couple spots in the engine bay where the paint had worn through for some reason, and repaired/glued some damaged plastic bits that have been knocking around since the same accident. And everything I put back in the car got throughly cleaned, because holy crap.)
Definitely something that is probably easier to do with a lift. And definitely something that is probably easier to do if you remove more parts than the guides tell you to. All the 7mm fasteners on the bottom of the car were rusted and rounded down to about 6.5mm; the only thing I had that would turn them was a 4" long 7mm box wrench that I think I stole from my dad about 20 years ago. The 6 screws that hold the cover to the fenders are accessible from underneath - but would be a lot easier to get at if the car were about 8 feet up in the air and the wheels, splashguard, and air intake/filter were removed. I managed, but I was pretty tempted to "mod" it so the screws went in from the top on reassembly. (I decided not to, mostly since I was tired and hungry.)
Incidentally, these guys do pretty good work, and their eBay store sometimes has sales. (My bumper cover was $163, painting and shipping included, which is less than any scrapyard I could find.):
http://www.mbiauto.com