Quick Summary: Don't record more than 30 minutes at a time--it will be too cumbersome a document to read otherwise, unless you plan to create several chapters in an e-book or it is part of a larger body of work.
As I have transcribed articles for various Internet marketing experts, real estate big wigs, and teleseminar gurus, I've noticed something quite interesting. They lose me after about 30 minutes of their "expert" audio/video. In spite of the fact that you can cram a whole lot more useful information in a one hour or a 1 1/2-hour audio file, you're just going to lose people along the way. They'll be dropping off like melons off a cart on a bumpy road. That is especially true when your audio/video is transcribed into a document.
A 30-minute audio recording will render about a 13-page document. From my perspective, I can tolerate reading 13 pages at one sitting. However, your average reader today who often reads on an 8th-grade level or below will take longer to read 13 pages. People who speak and read English as a foreign language will even take longer than that. Others are used to short synopses or summaries on various Internet sites and blogs and don't have the patience for longer articles. As I mentioned in Insider Tip Three, considering your audience is crucial, so you need to remember these aforementioned groups when you're planning your audio/video or article.
If your recording is an hour or longer, it will produce about 26-30 pages once it has been transcribed. That's a fairly long document to weed through for most people. I would say unless you plan to make your document into an e-book or a printed book with chapters of some sort, you're better off sticking to the 30-minute rule.
There are always exceptions to the 30-minute rule, for instance, sermons, which are often a bit longer. That's to be expected. However, if you're writing for the Internet, keep it short and sweet. Use your words carefully and succinctly--they will cost you in the end.