If you have a really short credit history (less than 5 years), you need to be aware that applying for multiple cards at one time can be risky to your credit. If you are going to need to get a car loan or mortgage soon, it might not be worth the risk.

Getting free travel can be seductive, but it's not worth jeopardizing your credit. Chase has been cracking down on high risk behavior, regardless of a person's credit score.

If you don't foresee needing any major credit/loans in the next couple of years, then it would probably be okay to apply for a couple of cards.

Also, Citi handed out 1099 forms for miles associated with opening a bank account. I don't know how this might apply to Fidelity, but it is worth looking into. Citi valued its miles at $0.025 per mile. At that value, 50k miles would add $1250 in income to your 2012 taxes. In the 25% tax bracket, you would have to pay $312.50 in additional taxes for those miles.