The National Congregations Study report from December 2015 (page 5):
"The NCS shows . . . an increase in . . . congregations that claim no denominational affiliation. Unaffiliated congregations increased from 18% in 1998 to 24% in 2012, and the share of churchgoers in those independent congregations increased from 10% in 1998 to 15% in 2012 . . . Non-denominationalism occurs mainly among white evangelical and black Protestant traditions, with 30% of white evangelical Protestant and 25% of black Protestant congregations claiming no official denominational connection in 2012. Independent congregations also tend to be newer than others, with the median congregation founded only 25 years ago versus 82 years ago for affiliated congregations."
One comment about non-denominational churches is that they have "congregational" polity. That is, they are are independent as opposed to being "connectional." Baptist and Pentecostal churches are quite similar to nondenominational churches in that they too are usually "congregational" meaning the local church makes virtually all of the decisions. The good of churches that are "congregational" in polity is that they can be nimble and relate well to the local culture. The "connectional" churches often get their guidelines from denominational headquarters which are sometimes dated and irrelevant. However, "congregational" churches can become "cults" because there is little outside accountability. They often don't realize that they need an "association" or "denomination" until a pastor leaves or there is some other crisis. Whereas "connectional" churches have a structure designed for stability and perpetuity.
I urge nondenominational churches and churches with "congregational" polity to find best practices from other denominations. I think especially here of good policies regarding handling accusations of sexual abuse rather than winging it. It is ignorant and arrogant to flout one's independence as a congregation as if you couldn't possibly learn from other congregations. 1 Cor 14:36 NIV: "Or did the word of God originate with you? Or are you the only people it has reached?"
Another way for nondenominational churches to learn best practices is for their ministry staff to get theological education. I highly encourage nondenominational churches to have many staff get seminary training so they they nurture a "deep bench" of wisdom from which to draw. I worry about megachurches where only the founder and a teaching pastor have theological education and call the shots and the rest of the ministry staff "execute" their orders. What will happen when the founder falls, leaves, or dies? Why not have lots of ministry staff up and down the organization get grounded in the wisdom of the church globally and historically? Why not have a 30 staff who can pick up the slack rather than one or two more designated hand-picked successors who are teaching pastors?
A nondenominational congregation can also join a denomination that supports congregational polity (Converge Worldwide, Evangelical Free Church, Evangelical Covenant Church, CCCC, Southern Baptist Convention, Cooperative Baptist Fellowship, Assemblies of God, Vineyard USA, etc.). They can provide support and advice if a crisis should occur regarding abuse, finances and can provide assistance after a pastor leaves.
On the other hand, denominational churches, that is churches with episcopal or presbyterian polity, should beware of hampering local effectiveness of congregations with bureaucracy and red tape.
Note too this from the National Congregations Study (page 11):
"Multisite Congregations. The development and proliferation of multisite congregations is an interesting recent development in American religion. Overall, 3.4% of congregations in 2012 were multisite; 10% of churchgoers were in those congregations."
A number of these multi-site congregations are "nondenominational." (We could access the data at the National Congregation Study website and find out how many). In some ways, those who attend nondenominational multi-site congregations are part of "denominations" in that they are guided from a headquarters. In other words, Willow Creek Community Church has lots of sites or campuses. Willow Creek is not a denomination but the offerings taken at a campus go to "headquarters" and are distributed to other campuses. So Bill Hybels is the functional "Bishop" or the Willow Creek Elders board is the "presbytery" and the Campus Pastors are the "parish priests." But as we have seen by the implosion of churches like Mark Driscoll's Mars Hill in Seattle or the practice of some megachurch pastors setting the secret salaries for other megachurch pastors, often times megachurches fail to have governing practices for succession and accountability that are adequate. Despite the fact that megachurches may use the "latest business management practices" as described in Fast Company, they should not delude themselves into believing they are "just as good as a denomination." Instead, megachurches too should be encouraged to associate with a denomination so as to benefit from the accountability and practices of an entity that is designed for long-term congregational health beyond the inclinations of one congregation.
I should say that I like multi-site churches and megachurches. My main concern is the one listed above: succession, accountability, and transparency.
Non-denominational churches are also explored at http://www.hartfordinstitute.org/ http://www.hartfordinstitute.org/cong/nondenominational-churches-national-profile-2010.html
On succession, see also:
Andy Rowell @AndyRowell 
