As noted above, various house churches above should be demarcated one from another. Christians, such as those in China, meeting in this manner by necessity are not committing a wrong. Denominational church plants meeting in a home certainly are fine as well. What we are dealing with here in the states with the "house church" movement, however, are a bunch of malcontents, self-important "teachers", and folk who despise being under anyone's authority other than their own. They have local churches available in which to fellowship, but for one reason or another have found themselves too good for any of them. Excuse me if I may be so bold, but having had our chapel disrupted by at least five or six of these groups in various ways, I do not think my evaluation to be too far off the mark.
Common themes among them all (and I am really amazed how many of these groups are out there, I'm still finding more of them all the time):
1. Usually (but not exclusively) lead by headstrong, sepratistic, yet thoroughly untaught men (this third point actually is exclusive), all of whom see themselves as having a special gift to teach.
2. Related to the above point, they all despise seminaries and look down upon men who have received their training from "the dark side". Seminaries produce nothing but spiritually dead academics, and this really frustrates them, because the spiritually dead academic seems to know his Scriptures better, and can regularly refute their fallacious arguments from church history, theology, and Scripture with a thorough knowledge of these subjects, and to top it all off these seminary trained fellows will even bring out their Greek and Hebrew guns on occasion (all of which may be self-satisfactorily defended against by way of a superficial use of a Strong's abridged concordance...)!
3. Because they have no training, and therefore no "skilz", they cannot really preach. This is covered up by asserting in grand post-modern manner that preaching is too "preachy", and overly authoritative. Therefore we only have "talks", which are nothing more than half-baked devotional thoughts. I wondered for the longest time why people kept telling me after my sermon that they really liked my "talks" - now I know. They had never heard a real sermon, and had nothing other by which to label one. People really like this style of teaching in the house group atmosphere, because it makes them feel cozy - no searching and penetrating exhortations found here (unless it is the occasionally required group grovelling - "boy, we all fail like this at times with our wives, don't we?") Even more important a failure, however, is that there is often not a clear and ringing proclamation of the Gospel.
4. They all despise Calvinism/Reformed theology.
5. They all despise any formal church government (i.e. any outside source that would call them to account).
6. They regularly get sick of themselves, divide over some really petty reason, and start at least two more home groups, each of which are headed up by the man who left because his teaching gift was not being properly recognized, and each of which consist of one family (that belonging to the man whose teaching gift was not being recognized). Not to worry about that last point however, because they know that before too long there will be at least a couple of people who will drift in after breaking away from another home group, and thus the cycle will begin yet again.
7. (at least for those here in the state of Oregon) Dave Hunt is their Guitar Hero!