Just make sure the output is at least 1 mAh.
That is the one of the most confusing and/or ignorant statements I have ever seen.
mAh, or milliamp-hours... that's talking about capacity, not 'output'.
From that, I would then assume you meant to leave off the 'h' so that you would have a current (in mA)... in which case 1mA is pretty near nothing. I can get a 1mA current by sticking one end of a wire down my pants and farting.
So, what I believe you meant to say taking that into account, is to make sure the output is at least 1A... or 1000mA, like has already been stated in the thread?
I can use google nav and 3g... streaming pandora with the screen at full brightness and still charge the phone with my 700mA hardwired microusb charger (chopped up 700mA microusb car charger sloppily spliced into the cigarette power accessory feed).
Long story short, if you use a 1000mA charger, you shouldn't have problems unless your phone starts getting really hot (charging faster heats stuff up more), as the phone will stop allowing you to charge once it reaches a certain temp threshold. Also, unless you are charging at over 1500mA on the stock battery (greater than a 1C charging rate), you won't significantly reduce your battery's lifespan (# of charges until failure).