I got one of those recently, the MB100.
It's absolutely fantastic. It has a few bugs (see Pixel Magic Forum) but nothing I've found to be too serious. They seem to update the firmware regularly so that's good.
I, like you, was also thinking about putting together a HTPC but couldn't be bothered with all the hassle and configuration. Not to mention that the MediaBox uses considerably less power.
It has every connection you could possibly want. I have it connected to my plasma with HDMI at 720p and the picture quality is great, especially WMVHD stuff but unfortunately there isn't much content in that format around. SD stuff is upscaled pretty well also.
As for noise, the unit itself is silent as there are no fans. However I have installed a 500gb disk into it that produces a slight hum but not noticeable when playing stuff. I have ripped all my DVDs directly onto the hard drive without any compression (ISOs and VOBs) and they play perfectly.
I don't do any streaming so can't advise on that. The downside to this unit is that it won't play any h.264 stuff and the price is a bit steep.
I find the user interface simple and intuitive (download the manual as it has some colour screenshots). Oh, and the remote is also better than usual, it has a backlight.