As a United Premier 1K you receive six systemwide upgrades per year, which can be used to upgrade United flights in select fare classes at the time of booking pending upgrade availability. All you had to do was book a minimum of a “W” fare to upgrade from coach to business class, or a minimum of a “D” fare to upgrade from business to first class.
One of the other cool things about these systemwide upgrades is that they could also be used to upgrade Lufthansa flights on a space available basis on the day of departure. The process was a bit more complicated since you had to call Mileage Plus to request a paper systemwide upgrade which they mailed to you, and then you had to bring it to the airport (as opposed to the process for upgrading a United flight, which was electronic).
Historically they could be used to upgrade Lufthansa coach fares to business class assuming you were booked in the “V” fare bucket or higher, which is just a bit higher than the minimum fare required on United. But the really cool thing was that you could use them to upgrade any revenue business class flight to first class on Lufthansa. So while United only let you upgrade from “C” and “D” fares to business class (more or less full fare), you could use those same certificates to upgrade to first class on Lufthansa on a discounted business class ticket (like “Z”). Naturally this was a really valuable benefit for many, given that it’s not unusual to see $2,000 discounted business class fares between the East Coast and Europe, which could be upgraded to first class through this program.
Well, it appears as if the policy has finally changed. New Lufthansa systemwide upgrade vouchers issued by United specifically exclude “Z” and “P” fares from being upgraded to first class, as you can see here. That being said, if you had a previously issued systemwide upgrade that doesn’t have that exclusion, they should still be usable on Lufthansa on discounted business class tickets through September 1, 2012. I suspect this policy change has more to do with Lufthansa than United, given that they just announced a policy change whereby “Z” and “P” fares are no longer upgradable to first class, even for their own members.