How long is too long? Or, at what length does a blog article become unreadable by the average reader?

I'm working on production of a local music blog, and I've found that a lot of my bloggers are transcribing 30+ minute interviews into 7-8 (or more) pages worth of text. We haven't gone live with the site yet, but upon initial brainstorming, this seems a bit long for me. I have a better attention span than most when it comes to reading long interview blogs, but the subject has to *really* grab me for me to read it for that long, because if nothing else, I'm typically reading on short breaks between actual work, and very rarely just sitting down for the sole purpose of perusing an article. I did a bit of basic google searching on advice on the subject, but was rewarded with very few useful results, so I thought I'd just ask the question and see what people thing.

So, generally speaking, if you are interested in a subject matter on a hobby or even professional level, how long will you spend reading one specific article / interview that is not required of you, but rather you're just interested in?

And if you have links to any relevant research, I'd be happy to read the data on that as well!

Thanks