@sammy2 FYI... I recently got my hands on an acquaintance's mhl adapter and usb otg cable to play with using my galaxy s3. The smart dock mentioned before enables using both types of connections at the same time, but still too pricey for me.
MHL... so this actually works fairly well, connect hdmi cable to adapter and tv, plug charger cable into adapter and outlet, then connect to phone... what's on your phone mirrors exactly on tv.
I tried playing video from several sources... Avengers HD download (came free with phone) playing in mx player, looked great. Also played some files over the network (no transcoding) and looked great as expected. I don't have plex, but I tried Remote Potato server with the Remote Media Center app and again worked as expected.
Netflix, streamed fine, but the output is somewhat low quality and displayed as 4:3 on the tv, widescreen on the phone. Seems Netflix has this restriction for external player with the mobile app?
Youtube worked great, switching to 1080p and quality on tv was htpc equivalent.
Tried Xfinity (comcast) TV player app, which plays online on demand content... however, the app has a no external display feature, so it won't work while connected to mhl.
Other notes about using MHL... it does require the charger cable being hooked up to the mhl adapter to work, this does show your phone as charging. However, the drain on the batter is higher than the charge coming in, so the battery will slowly drain while using the external display. Also, the phone displaying on both the phone screen and the external display can over time cause the phone to heat up.
I did some reasearch, both of these issues can be significantly reduced using an app called Display Standby... it does require ROOT, so I haven't tested it. It disables the phone's screen without putting the device to sleep and allowing video/audio to continue to play as well as the touchscreen features to continue to work. Claims to reduce battery drain by quite a bit and cut down on heat build up some, though the gpu will still likely be generating heat.
USB OTG (on the go)... nice option to have, worked right away with my wireless usb mouse and keyboard. Tried an xbox 360 controller for fun, worked too, but any games apps would most likely need mapping/configuring functionality to work properly. Also worked fine with connecting usb thumb drives or hdd drives... with a usb hub you can connect the mouse, keyboard and drives all at once.
Unfortunately you can't use both mhl and usb otg cables at the same time, you have to have the smart dock for that. If the dock was cheaper, I would definitely buy one.