This is from a post on the UA board. A little dated, but:

Originally Posted by Randy Petersen

For the record, coming out of 2004 these are the numbers:

- 535,000 members were Premier level
- 239,000 members were Premier Executive level
- 46,000 were 1K level
- 18,000 UGS; 8,000 to entice business, 10,000 that spent $20,000 or more

As a comparitive stat, approximately 11.7 million members are active in the Mileage Plus program. That is 11.7m ACTIVE members. There are around 60 million actual MP members IIRC.

Note that the secret level is called "United Global Services" and I heard that it is now has posted that a UGS member who spends $50K with the airline is guarunteed to get UGS level again the next year.