I have the QUMI and waiting to hear more about the Acer (to see if it's any quieter than the Optoma) and will get one of the 500 lumen models as well.
this topic has been beaten up pretty good since the QUMI was announced. I think for video, pixel structure is less noticeable on the QUMI on my 142" high power screen vs. the Acer 5360 where the pixel structure is quite noticeable compared to my 1080P projectors.
I probably wouldn't use it for a secondary PC display, but for presentations like powerpoint, I don't see a problem with it. 720P is kind of beat for corporate presentations anyway, especially if your viewing spreadsheets, etc.
IMO, these projectors (qumi and 500 lumen models) are a great breakthrough compared to the previous LED's which were seen as dim toys. These projectors are actually usable for watch TV, some movies, etc.
I don't expect the same image quality as my Sony HW30 or JVCRS50, but then again, I can't fit either of those in my laptop bag.