This is a good one. I'd recommend reading The Innovator's Dilemma by Clayton M. Christensen. It provides a lot of insight into how companies get so invested into what they've built that they have a tough time identifying if/when to adapt to emerging technologies, behaviors, and helps identify how organization can better identify those opportunities.

The ad income will vary drastically based on who is viewing your content and if you can have your inventory direct sold or if you're using google to fill it and if you have an MCN taking a cut, etc. But let's break it down:

ADS
Let’s assume you're part of an MCN, and you're getting a $5 CPM (probably likely). YouTube takes 45% off the top, and then you have to give a percentage to your MCN (let's say 25%). Here's how that would break out:
$5.00 CPM
$5.00 CPM x 55% to channel (after 45% goes to YouTube) = $2.75
45% of views are monetized ~ $1.24 (odds are most of your views won't have ads)
25% goes to MCN ~ $1.15
Total to creator ~ $1.15 per thousand views

OTHER REVENUE OPPORTUNITIES
I literally just did a blog post about this, you can read that here (http://brendangahan.com/?p=343). But, long story short, YouTube can be a great platform to cultivate an audience, and from there you can channel the audience to any number of revenue opportunities (Merch, etc). Hope that helps.

Agreed. Pownce and FriendFeed were both hailed as Twitter competitors in the early days. In 2008 Twitter was consistently plagued by downtime as they had trouble scaling. However, the service was simple and easy to use and they did a great job getting early digital influencers and celebs onboard evangelizing the platform. When Twitter first got started they also had a suggested user list and recommended lots of famous people and digital influencers to follow. This created a bit of a self-fulfilling prophesy - those on the list would evangelize twitter helping to funnel even more people in and boosting their own popularity, etc.