The only United Airlines promotion I know of was the one for 2,000 Clickmiles, not 750.

The only other two that are for 750 that I know of are:
http://www.clickreward.com/TWAapril01 http://www.clickrewards.com/deltafeb01

I suggest using the "search" feature in the upper right hand of the Flyertalk Forum. You can then find most, if not all, of the answers you seek. It's what I used just now to post this answer.