So it really comes down to the question of are these Pico projectors really viable for important (or unimportant) presentations? I'd still say, you are iffy with the 20 lumen and under ones, but, if you know your client, and the cool factor will be an acceptable alternative to a bright dynamic presentation, then you are fine. Otherwise, though, take a close look at that Optoma PK301!
Last year I said I really didn't think any of the pico projectors we reviewed could actually do a really respectable presentation - primarily due to lack of lumens, and overall picture quality. Boy does one year make a difference, which, again brings me back to the 50 lumen maximum Optoma Pico PK301. It may not be up with a traditional portable yet, but, what a huge improvement. You could learn to enjoy this projector's picture quality - as long as you aren't demanding home theater quality!
Several of these projectors, will allow presentations from composite video, memory card, USB, or downloaded into internal memory, and you won't need to take your computer along for the ride. That makes sense, in terms of the ultimate portability.
For example: The 3M MPro150 has a VGA port. No need to convert everything to jpegs and video clips, just bring your computer, and hook it up. For that reason, the MPro150 is a "real" projector in the sense of capability, even if lower resolution than any regular small portable projector.
The Optoma, last year, could only handle doing presentations from composite video or USB, and it came with software to convert files like powerpoint to jpeg images. This year, though, the Optomas are far more capable, including an HDMI input. In other words, this year, fully ready for business and higher res, compared to last year's first generation pico.
In fact, this year, every pico (and the LG pocket) projector we worked with, could take a computer signal, except the P1 Jr., which has a media player onboard so you can present from jpg and other file formats.
Bottom line: Yes you can use these projectors to do one on one (or one on two) presentations, in a darkened room. If your portability requirements demand the absolute minimum, these will work for you.
To me, the jump to about 50 lumens, from 10 or 20, goes a long way to making these projectors viable and serious products. 50 lumens - Optoma PK301 - on AC or external battery, can actually do a respectable image, at a modest - but respectable size - such as 50 inches diagonal. That's certainly big enough for a conference room group, even 10-12 people if seated close enough for that sized screen. Certainly 50 lumens will do a fine job in front of 2 or 3, as long as the lights are off, or low, and under control.