I have to disagree with "...getting to the top tier of one program before establishing status with another". It depends on your travel patterns. Leisure or Business? Where are you going, how often, and when? If you know one airline can meet most all your travel needs, then sure, getting to the top there makes sense. However, if you fly a lot for business and to many different destinations, a single carrier may be very inconvenient. Better to have mid-tier status on two airlines you will use a lot, then top tier on one and nothing on the other. Better yet is mid-tier on two airlines and lowest level status on another. Almost nowhere you can't get to in a reasonably convenient manner and at decent times.

Personally, I find myself on US a lot for leisure (family/friends on the east coast) and Silver status works very well there. For business I use AA and UA and hold Platinum status on AA and 1K on UA (dropping back to Premier Exec in March). With the UA/US merger, it is likely that I will spend more time on UA and thus may shoot for 1K again this year. With another 100,000 AA miles, I will be lifetime Gold (lowest level) and won't have to worry about status there anymore.