Quietlion is quite correct. I'd like to add that this competitive comp is usually given for the partial year that it is given, and the following full year only. After that they expect you to qualify like everyone else.

Most all of the airlines do this.

United (and I'm sure most other major airlines) also comp Premier and Premier Executive levels to top flyers for some of their biggest corporate customers. As above, usually for a trial period.

United also usually comps PE status for the one year after an existing PE drops below the required requalification mileage.

Finally, United offers Lifetime Premier Executive status to their deadbeat Million Mile Flyers.

letiole makes a good point that you (and even other 1Ks) are competing with 1Ks. I'd like to add that you are also competing with Sales Department Upgrades, Customer Service Upgrades, Positive Space Employees and Retirees, VIPs, C or F International Connecting Passengers and the general Mileage Plus Member that is using miles to confirm an upgrade in advance. And let's not leave out that most dreaded enemy of all frequent flyers...the full fare Business or First Class passenger!

And of course, the aircraft you travel on and the markets you fly also have a major bearing on upgrade success.

Which is probably why some consider United's upgrade policy rather frugal. United probably gives out only enought upgrades that they figure you have a chance of redeeming! They probably figure that you'll be a happier member if you've been able to use up the certs that you have been given, rather than be a mad member who is stuck with expiring certs that they weren't able to use!

As bad as I make it sound, as you can read in other threads, PEs have a pretty good success rate overall. And I think things are going to improve for Premiers and Premier Executives substantially in the future because of:

United's Economy Plus: I think fewer pax will be using miles to upgrade if they find this new product to their liking.

Electronic Complimentary Upgrades: Rumored to be coming this year and similar to Delta's, this will replace paper certificates and have greater accountability for Agents. This should effectively close most of the loopholes that letiole mentions above. Some 1ks may find their upgrade opportunites actually declining because of this, but it should be good news for most Ps and PEs.

As always (unless you're on the same flight as me)...Good Luck!