In my experience, it depends on the shoe.  I only got about 300 miles out of my Mizuno's road or trail.  I am currently wearing Inov-8s and am getting around 400 miles out of them.  Some people are able to wear their shoes forever.  A friend gets 500-600 miles out of the same style of Inov-8s.  When I start getting a grumpy back and knees, it's usually time to rotate in a new pair.

I don't like buying stuff.... so I tend to try to get a lot of miles out of my shoes.

I haven't run at all this year (boo), but I have about 930 miles on a pair of Adidas Adizero Tempos (mainly road and firm trails), 800 miles on some Mizuno Wave Inspires (road and trail) and 650 on some Mizuna Wave Mushas (again, a mix, but mainly trail).

I don't recommend trying to get 1000miles out of a pair of shoes, but it can be done.  Once they are past about 500 miles, I tend to reserve them for easier runs on softer terrain and use my newer shoes for hard / road runs.

For me I wear out the uppers long before the soles are worn out of my trail shoes.  Depending on the shoe I get 400+ miles on a pair.  Some are close to 600 and still going strong for trail use.  The trail surface I normally encounter is dirt, sand, packed sand and leaves though.  If you encounter a lot of rocks, your mileage may definitely vary.

My trail shoes wear down in a completely different pattern than my road/treadmill shoes.  I have been a wearer of Cascadias for several years (4 or 5 pairs), and the front tread wears down MUCH faster than the tread below my heels. In fact, it appears like it is un-touched. I tend to run on my toes when on trails. 

My road/treadmill shoes wear down a bit more evenly, as I tend to strike the mid-foot first. 

I use trail shoes on technical trails only and my road/treadmill shoes on roads (duh), treadmills (double duh), and rail-to-trail runs.