In a nutshell, SocialSpark, from what I gathered after reading what Andy Beard wrote, is a Advertiser Social Network that will allow Advertisers to choose blogs for their Advertisements base on real “blog power” and not on the superficial Page Rank. Quoted from Andy’s post,
Accountable Analytics - current methods for advertisers to present the viability of advertising on a particular blog basically… suck - you name it
* PageRank is worthless - you can have a site with a PageRank of 7 and almost no traffic, and at the same time have a PR3 blog that gets thousands of visitors a day.
* Alexa & Compete are easily gamed and are highly biased in many verticals such as web design, SEO and technology, and the sites people in those industries frequent.
* Quantcast would be useful… but very few sites include Quantcast code on their sites, even those who are marketing aware.
In view of this recent developments, many bloggers who does paid reviews and other form of Advertisements jumped with glee, with the opinion that finally someone has come forward to do justice to the tight slap that they got from Google recently. Indeed, I too felt good initially. but that good feeling was short lived.
Smaller Blogs Will Become Redundant.
If you look deep enough, you will realise that in future, getting Advertisers to choose your blog will be tougher than biting into a piece of leather unless you have a blog that has thousands and thousands of visitors daily.
At present, even if you have a blog with 0 page rank, you will still be able to write some low paying reviews that pays a nominal $5 per post. Speaking from a money making point of view, those who works hard enough makes a decent income from their blogs that has no Page Rank or visitors whatsoever. This has come under harsh criticisms from many quarters questioning the echticity of such blogs. This problem will be effectively dealt with once SocialSpark comes into play.
There is no joy for a small blog like this. No doubt, the release of the Google buckle that has been tightening by the day will be a relieve and the dependence on money making blogs on the vital Page Ranks does in a way augurs well for many, SocialSpark might also actually be killing those low traffic blogs faster than the Page Rank demotion that they faced earlier.
There are no indication at present as how many visitors a day is enough to please an advertiser to have your blogs do a simple review for them, but I think you don’t need to be a nuclear scientist to know the fact that it is of course, the more the better. This time around, it will be Advertisers that are really looking for blogs to advertise their products rather than wanting a Linkback.
Bearing this in mind, in the next few weeks, we can expect to see a flurry of activities from blogs finding ways to increase their readership base. The floodgates to the playing field has been opened, but how many will succeed in creating a readership base big enough to be on a level playing ground with the big boys?

I don’t think Social will work for many small blogs unless the advertisers wan geo-targeting but it’s no harm to join.
I seriously didn’t know about Quantcast… at their website browsing now.
Costa, I do think there’s 2 kind of advertising. FIrstly word of mouth…. then advertisers will look for heavy traffic blogs.
Secondly, for SEO purposes so the company name comes up in the search engine.. advertisers will then look for PR.
Either way, many net surfers are still using Google. If your company name don’t come up in their search engine, what’s the point? Unless everybody switches away from Google (not only disgruntled Paid post people and PR victims), PR will still reign.
Ditto what helen said, you need that pagerank to help visitors find you in the first place, but hopefully it won’t be the be all end all of getting advertisers.