Playback is a nice tool that allows you to stream content to other devices. It can be used to stream your videos, music and photos to devices like Xbox 360s, Playstation 3s and pretty much any device that supports uPNP. When you activate Playback, every device that supports uPNP will detect it and you can start playing video instantly.
Formats are always an issue when dealing with media playback devices. Playback does not transcode your files, it simply streams them. Let me use the Xbox 360 as an example to explain this to you. The 360 does not play MKV files natively. Thus, if you want to watch your MKV movies on the 360, you have two options: convert the files or use a transcoder (which is converting + streaming, an on-the-fly solution). Playback states that it supports the streaming of HD MKV files. That is not entirely the case. It comes with a video converter built in that lets you convert those files to MP4 before you share them with your console or media playback device. It doesn't transcode them, though.
In my testing, Playback worked flawlessly. It is an excellent solution and it is really well designed. My Xbox 360 detected the media server installed on my Mac instantly, and I was able to play SD XviD files over my wireless network with little to no buffering. The quality was great. If you want to watch your videos, music and photos on the big screen but don't want to be moving your computer around, Playback is an excellent solution and it is not very expensive. However, keep in mind that it will not transcode media and that it doesn't support SRT subtitles.