I think in today's internet generation, trying to sell anything with a clumsy video of anything more than 3 minutes is essentially suicide. If you're talking about a funny video, maybe 3 minutes is too little. But when you want to sell folks stuff and you make it boring and draggy for them, it doesn't get any worse.

Our vid on the homepage is a mere 1m30s, even the most effective (funded) projects on kickstarter are short and sweet, so that's definitely the way to go.

You could check out some awesome product videos over here.
Demo Videos: What are some good examples of startup product demo videos, and who made them? - Quora

- Alex

If you get bored during the video then either:

a) you are not the target market for that video and so you can't relate to it.

or

b) they have done a crap job of selling

It can only be one of those two things that causes you to get bored during a sales video.

If you are truly interested in something you could easily sit there and watch a 30 minute video. It all depends on how targeted the message is to you.

Then the video is doing a good job filtering someone who is potentially not interested in the offer.

Will makes a good point, I have watched long sales videos because the product had interested me, I have also gotten bored very quickly. So really it isn't about liking them or not, it is all about your interest you initially have in the product. If the marketer done his job per-sale then your watch it if they didn't, your move on.

I think the content , length & presentation of video highly depends on your targeted viewer. Take it like this if you are promoting an product to help newbies to make money online who have no idea how things go here & have no experience of online marketing than may be that 10 to 15 minutes long fancy video showing different things & a larger than life picture will work for them But if you are promoting something where your targeted viewers are way mature than your video should be made in different way where there should not be any BS only straight to the point showing some inside visuals of the programme & things like that....
So consider your target viewer & made an video according to them not how you wanna make !

Then the problem is not the length, but their poor sale script not addressing what their prospect wants to watch.

Like any sales page (written or video), it depends on A) whether you're a targeted prospect and B) the quality of the pitch copy.

The sheer length is not really that relevant. For example: would you rather watch a good 3:00 hour movie or a bad 1:30 hour movie?

I have a site selling a $500 product via a 54-minute sales video that converts at 1.72% from cold traffic (not bad at all for a $500 product).

Yes, those videos are effective. I worked as a CSR for a guy who launched a product that had one of those videos - I think his was around 45 minutes long, and it only had a vague explanation of what the product really consisted of at the end of the video. No specifics ever. But his target was newbies to Internet Marketing who wanted "the dream," and yes, it was a successful launch, and yes, a lot of newbies purchased that and more just from watching the video.

Selling a dream is much more effective than selling a plugin - and that was what he was really selling them, a simple plugin that created a simple sales funnel. You can buy that here for under $20. He sold his for $97 with an upsell of backlinking features for $197. And he got it, and nobody who made the purchase knew what they were getting until AFTER they purchased.

If you are using a Video on your sales letter, you could definitely increase your conversions, however I'd personally prefer the video to be under 3 minutes or so.

It could really boost your earnings.

I understand what are you talking about, i feel the same.
On the other hand, we can't argue with facts, and those videos sells great.
(Most of top selling CB product has long boring videos on there sell page)

The right product needs to address 3 things:
1. Message
2. Market
3. Match

If you are the right person, if won't be boring.

Shorter videos are indeed much better than those long ones that you see so many Internet marketers make trying to sell their stuff with all those hired actors, rented sports cars, and borrowed mansions and such.

All you need to do in a video is to get straight to the point, don't show any screen shots of money earned, and just talk about what it is that you're offering. If you do that, then people will be more likely to purchase than if you were to make some huge video that spans several minutes trying to sell them on something.

depend on the market and targeted audience