How long should a demo reel be?
What types of things are employers looking for when viewing a demo reel?
It all depends really. First and foremost, the idea of having a reel is to sell an employer on your skill set, and show them what you can do for them. So you really want to put your best work in there. If you have a reel that's full of incomplete or glitchy samples you won't impress a picky employer.
You also want to showcase your main talent, but show versatility in your work. IF you're primarily a motion graphics guy, but you've done some really nice 3D-character animation, try and implement some of it into your reel. There are some renaissance-men out there that have so much work from different areas of production that they have multiple reels showcasing different skills. There aren't too many of them however.
As for the duration, I've heard the general rule of thumb to be anywhere between 1 and 3 minutes. Employers are way too busy to watch an epic 10 minute reel, but that shouldn't stop you from including your best samples from a 10 minute piece. You can also provide full sample per request or on a youtube account.
I would also recommend having your name and contact info clearly visible at the beginning and end of your reel (my contact info is only at the end, but my name appears in the beginning). It's also nice to have s theme to your titles. Check out my reel here:
And this guy's:
You can see what I'm talking about with the slates in both of these. Just make certain that the person looking at your reel has enough time to tell who you are.
As for music, choose something that complements your style. People generally like to avoid anything with lyrics, but I love the music I chose, and it's repetitive enough that the vocals aren't distracting. Also, I wouldn't worry about attaining rights to music used in your reel. You're selling yourself, not your demo reel (in fact you're giving that away). It's nice to put a quick heads up credit for your music but not necessary.
I hope that answers your questions. My best advice to you is to get out there and absorb as many samples as you can. See what other people are doing and get an idea of how you want your reel to look.
Good advice... they used to say 6 minutes, but I agree, around 3 minutes is probably better these days. Make sure the information is relevant... don't include a whole bunch of motion graphics work if your going for a camera man job.
If you're doing a reel to get freelance work, or be self employed, consider doing a reel about yourself and your services rather than a reel showing off a bunch of eye candy.
Actually, this might be a great way to get an employer's attention too... do a reel about why they should hire you, and let your skills rip... that would catch my attention. Unique.