My church is small, so currently it only has one deacon (though the hope is for more). Generally, it uses Strauch's New Testament Deacon as a guideline for the deaconate.
Their concern is for the care of the church, with an emphasis on the physical needs of the members and the church. Some things they are charged with are: delegating the physical upkeep of the building, handling our benevolence funds, and reaching out to members in need to figure out what is needed and how the church can help.
In our church, they go through training with the pastor (working through Straub) and then spend some time doing some of the deacon functions as a time of testing. After a while, they are brought before the congregation for a vote to determine if they are going to be a deacon of our church. They do not have term lengths.
Deacons are under the authority of the elders.
There are a few things I disagree with in regards to my church's stance on deacons, but by and large I like what they do.
Well yeah. So we look at the name, see where it is used in the Bible - it always describes a servant of one kind or another whether it's used as the office or not.
A lot of my thinking comes from Alexander Strauch in The New Testament Deacon. He takes a pretty hard line on what a deacon is and what he is not. I don't quite take that hard of a line, but I like a lot of what he says.
Namely: deacons should serve people, not things. (That's a crass summary, not a quote)