YouTube, the online video platform owned by Google, celebrated its fifth birthday on Sunday with the announcement that the site is now racking up two billion video views per day.

Google aquired YouTube for $1.65bn in 2006, but like many social networks, questions have been asked about its revenue generating potential. On Sunday, YouTube said that the average user spends 15 minutes a day on YouTube, and the company manages to monetize over one billion video views per week globally. But out of a total of about 14 billion views per week, the numbers don’t seem too impressive.

Still, YouTube claims that 94 of AdAge’s top 100 advertisers have run campaigns on YouTube and the Google content networks, which could mean anything, while partner ad revenues more than tripled in 2009. Google doesn’t break out YouTube revenues, but its partner network revenues climbed from $1.6bn in the first quarter of 2009 to $6.5bn in the same quarter in 2010.

It’s interesting to see how, according to the YouTube timeline, when the platform went mobile in early 2007, the angle of the growth curve for video consumption suddenly sharpens, suggesting that mobile had a significant effect on viewing figures.

Two billion videos a day is a lot of content and a good deal of that will be using up mobile network bandwidth. We recently wrote about the capacity crunch, but with a nod to the future, telecoms.com is at the LTE World Summit in Amsterdam this week looking at how 4G strategies will help solve all these problems.