Wireless video has been around for quite some time now, but many of us have struggled with the drawbacks that it brings. Compression, lag, spotty performance and other troubles don't always make for a great viewing experience.
Things are improving though, and if you really can't run an HDMI cable across the room then wireless is a great option that's finally starting to become (relatively) affordable. You can send a wireless signal to your TV from a computer, tablet, smartphone, set top box, Blu-ray player, or anything that outputs a digital video signal via wireless HDMI (here are a few systems, including one we've reviewed).
Watch out for: Picture quality can really suffer with wireless HDMI and performance can be spotty, as can continuous connectivity over longer distances.
It takes quite a bit of work to plan out a speaker setup when you consider a cable going to each speaker location, all heading to a receiver of sorts in a central location. That mess of wires can be avoided with wireless speakers and subwoofers. You can also skip the full spread of speakers (left, center, right, back left, back right, and subwoofer in a traditional 5.1 surround sound setup) and have just a simple bookshelf speaker or soundbar and subwoofer. Small, portable wireless speakers are great also for outdoor entertaining.
Watch out for: Although you'll unlikely hear much of a loss of quality in the wireless transmission (especially considering mp3s already suffer some quality loss), most wireless speakers are fairly small and value-minded. Their audio output is generally weak, but it's getting better.