First off, I would recommend getting a Citi Business card for 75000. That's what I did when the personal wasn't available for me (existing card).

And getting both United and Continental cards makes lots of sense. If you do that, then definitely jump on the Cont. Debit Card NOW before it expires Dec. 31. If you do them all, you can quickly get close to 100,000. Actually best to wait for the Cont Mileathon before getting that credit card.

Personally I go back and forth between adding miles where I want them the most (AA) and getting miles where they are easy to attain. Some months ago I decided to stop trying for Delta miles. I used up what I had, canceled my Delta AMEX before the annual fee was due and took my account down to 0. Then the Suntrust deal fell in my lap, got the 45000 business AMEX today, signed up AMEX singleidentity for 5000. Voila my Delta will soon have 175000 - more than any of my other accounts. And the process was nearly effortless.

Why not have the flexibility of miles in many programs if it's easy to attain?

I've been gathering miles all year while making only one airline trip all year. Seemed crazy at first (except that I am enjoying the process), and now I have at least four trips to make next year for weddings, etc. I enjoy knowing I'll be able to make all those trip for close to nothing dollarwise.