Yes I'd say about 20% of them get a well explained no, 20% get a yes based off something already happening, 10% get a yes on their own, 20% are things they can't comment on (active legal cases for instance), 20% get stupid responses, and 10% are really stupid petitions to begin with (like states leaving the union). More than anything I think the petitions let the administration know how to prioritize releases. It informs them what is 'hot'.

Some highlights:

Obama administration backs down on Marijuana Legalization: https://petitions.whitehouse.gov/response/addressing-legaliz...

Army Stops using monkeys (this actually happened in response to this petition as far as I can tell): https://petitions.whitehouse.gov/response/army-no-longer-usi...

National Guard Joint Chief of Staff created: https://petitions.whitehouse.gov/response/chief-national-gua...

This petition (and opinion polls probably) helped prompt the administration to appeal SOPA and PIPA: https://petitions.whitehouse.gov/response/combating-online-p...

This petition (and some campaign promises) have slowly resulted in increased digitization, recently the house put much of their data up in XML: https://petitions.whitehouse.gov/response/digitizing-federal...

This petition is well written if nothing else: https://petitions.whitehouse.gov/response/doubling-and-tripl...

These petitions happened at the same time as (though it's debatable if it resulted in) the president declaring he would not defend DOMA: https://petitions.whitehouse.gov/response/greater-protection...

https://petitions.whitehouse.gov/response/repealing-discrimi...

This petition coincided with a policy change on student loan burden reduction: https://petitions.whitehouse.gov/response/taking-action-redu...

No. It seems unfortunately another one of these initiatives, that pretend to take concerns serious - by putting them in a file. But it is a smart buffer to channel the voice of internet driven activism an direct it into a digital nirvana.

Good questions. I think they only promise to acknowledge the petition, not necessarily do anything about it. If they're raising the minimum number to 1 million signatures, I wish they would promise a bit more, though I don't know what.