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WHAT?!?!
As someone looking into a Mac Mini/Plex video streaming solution, I had no idea this was possible with a PS3.
If you all will excuse me, I've got some Googling to do.
To enlighten everyone:
PS3 is a very powerful machine. It has built in Bluetooth (so it supports Bluetooth headsets, keyboards, speakers and mice without any modification whatsoever) and is designed for use on a TV. The interface is very snappy although not completely perfect. If you're not comfortable using the gamepad to navigate it, there is an optional Bluetooth remote control which you can buy too.
Relevant to this forum, it's a Blu Ray and DVD player with the capability to stream video from your Mac or PC over a network (it has built in WiFi and Ethernet). You can copy files to the hard drive too, and if you fill up the hard drive or just want a bigger one they are very easy to replace - one screw lets you in and then it's just a matter of swapping the old one out for a new 2.5" SATA drive (like the ones Apple uses in MacBooks and which are very cheap). Doing this won't invalidate your warranty.
You can connect external drives via USB (there are two ports on the most recent consoles) or insert DVDs or CDs with files burned to them and again, copy them right over to the console's own drive.
If you live in Europe you can buy an add on called PlayTV which allows it to receive over the air digital TV (DVB-T, known as "Freeview" in the UK), pause it, record it, rewind it and generally do everything that Sky+ or Tivo can.
If you live in North America there is a video store which has a wide range of movie and TV show content. Prices are competitive with iTunes I believe, and the store is being launched in other areas (Europe) later this year.
There is also a web browser with Flash 9 included, meaning that it can play back videos from Flash enabled websites like BBC iPlayer and STV Catch Up.
All of that and I didn't even mention games yet. It's widely perceived to be the most powerful games console currently available and it has hundreds of games including compatibility with PSOne titles. You can buy games from the PlayStation Store or on disc.
I am stunned by the number of people who buy Apple TV when this is available for slightly more money and it does so much more.