Depends on the age of the site, their keyword density, the meta description etc. In terms of the backlinks then it shouldn't be too difficult to beat what they're offering over time. A good mix of video site submission urls, articles, social bookmarking sites and some high pr forum profiles should see you on your way.

It's the "a lot of them are unrelated sites" that matters.

The PR (as between 0, 1 and 2) is far less important.

Yes.

Depending a bit on what you mean by "handful", I suppose.

But when you fight quantity with quality, you win, and typically you win pretty quickly, easily and reliably.

(I realise this isn't what you asked, but there are loads of PR-0 pages outranking PR-1/2 pages in Google's SERP's, by the way, and when you examine their backlinks in detail, they're a very reliable indication that context-relevance is what matters).

very difficult to say. things to think about;

1. you are only seeing max 70% of the existing backlinks. even the very best backlink programs (SEO Spy Glass) can't see all backlinks. Google Webmaster provides the most comprehensive look but owners tend to keep these details private!

2. what is the on page SEO like on these sites vs your site? H1 tags, interlinking, content quality.

3. what type of backlinks are we talking about. Contextual, home page, footer, no follow. google putts different weighting on these.

4. do you and/or your competitors have your target keyword in the url? Matt Cutts has said they'll be reviewing their weighting of this soon enough but the fact is keyword density in your url does help.

YouTube - Does the position of keywords in the URL affect ranking?

here's the one I was thinking of, just couldn't find it earlier.

http://www.youtube.com/watch?v=rAWFv43qubI

I'm starting to think Matt HATES Viagra sites!!