Not officially affiliated with a particular party or candidate, SuperPACSs can raise ginormous wads of cash to promote "issue" advertising and outreach.
Of course, their position on said issues make it pretty clear which party and/or candidate they're supporting...
But while it was feared such SuperPACs could tip an election towards the party or candidate that could attract the wealthiest donors, the outcome of the 2012 election suggests they were self-neutralizing at best and counterproductive at worse.
The GOP seems to have sustained the most self-inflicted damage. This is not a reflection of either party's platform but rather the nature of the competition this year.
The Democrats had the advantage of a seated president with no intra-party opposition; the Republicans had to whittle down a field of seven candidates, each of whom had a battalion of media consultants/buyers in tow.
As candidates dropped out, these consultants/buyers had to do something, so if they couldn't glom onto another candidate's campaign, they drifted towards the SuperPACs.
And the SuperPACs welcomed them and followed their recommendations for media buys.
Problem #1: Since SuperPACs are forbidden by law from coordinating their efforts with established parties and candidates, there was no way to keep them on message. SuperPACs would run ads that worked against the official campaign of the party and candidates they were supporting.
Problem #2: Without a campaign manager to reign them in, SuperPACs would saturate media markets in battleground states. For example, the official campaign might not want to run more than one commercial per half-hour to avoid viewer fatigue; SuperPACs' independent media buys might bump the total number of political ads for a candidate up to three or four per half-hour. The chance to influence voters was undercut by a growing annoyance at a party or candidate even if they weren't responsible for the ad.
Problem #3: Despite their purported support of "issues" related to a particular party or candidate, in fact SuperPACs don't exist to support candidates, they don't even exist to promote the interests of their donors. Rather, they exist to line the pockets of the people running the SuperPACs. GOP leaning donors in particular were hard hit by PAC-men who took big fees to sell overpriced commercials at top dollar; by contrast the official Democrat campaign made much more judicious use of their advertising dollars, getting more media out for less money. (This is not to tout one party over another, just to point out the extremes between SuperPAC spending and an actual campaign.)
By chance of history, the Democrats came out ahead in the battle of the SuperPACs this year; 2014 & 2016 will be entirely different scenarios.
But I think the GOP's hard learned and very expensive lessons of 2012 are going to be a clarion to both parties. Expect SuperPACs to be severely curtailed in the future, if for no other reason than each party's self-interest in determining their own fate.