Pocket projectors are starting to ship. Two reviews posted within the last 24 hours: the 3M MPro 110 (around $475) and the Epoq EPP-HH01 ($229).
The reviewers' comments suggest that although the devices can be used, it is still early days. Light strength is still relatively weak and resolution is not optimal (especially for text). As a result you need a darkened room, put the device 1-2 meters from the wall to get an image of around 40-50cm.
It sounds like we need some patience for 2 things to happen:
  1. These devices become powerful enough that they can project a bright, big image. Until then, the laptop screen might be better. Maybe a compromise could work. A projector that is as flat/small as a laptop, but not quite pocket size that does meet minimum projection quality requirements.
  2. More interestingly, this technology is incorporated in a mobile phone, providing these devices with a big screen instantly. The first application will actually be a replacement of the mobile phone screen for let's say web browsing without the need for scroll bars, or viewing Microsoft Office documents for private use, or projecting the latest family pictures. Showing presentations to an external audience is still less obvious.