I think (and someone please correct me if I'm wrong) that Chaozhou / Chaoshan gongfu cha is the root of gongfu cha. Even in that style, I don't think there's one exact method that's agreed on by everyone. I outlined one method that I've seen at http://www.teadrunk.org/viewtopic.php?pid=75#p75
I do that this procedure (or its rough equivalent) could be followed on an everyday basis, and is practical (it sounds complicated, but it's not really that complicated and doesn't IMO contain unnecessary steps). Even when brewing other types of teas or following a slightly looser style, I tend to incorporate a lot of these practices into my tea brewing. I think gong fu cha has a big element of ritual in it (which is part of what interests me about it), but not as much ceremony, especially when compared to something rigid like Japanese tea ceremony.
Some general trends in Chaozhou gongfu cha, based on my own limited experiences / reading:
1) A small kettle is ideal (for quick heating of water), preferably the traditional charcoal stove / side handled chaozhou red clay kettle / olive pit charcoal, but many people seem to use metal or glass kettles these days too. In fact, everything (kettle / brewing vessel / cups / etc.) is small.
2) Amount of tea leaf used is generally pretty high. For roasted Tieguanyin, I have definitely heard volumes of 1/2 to 1:1, and some of the leaves (probably between 1/6 and 1/3, but the exact proportions and methods of building the pile of tea seem to vary) are crushed with the hand... keep in mind that the older style Tieguanyin was not tightly balled the way it is now... According to Tim, with most teas other than Tieguanyin you don't crush any leaves, with the possible exception of Feng Huang Shui Xian (not 100% sure about that one). I think it's typical for people in this area to use a lot of tea leaf with wiry teas also, but I certainly have heard of people who don't do this (Imen's teacher, for example). So my understanding is that a lot of tea leaf is typical, but I don't know if there's a hard and fast rule. I think this is a general trend even with other variations.
3) Traditional teas would be Anxi Tieguanyin (typically high fire), Feng Huang Dan Cong / Feng Huang Shui Xian (local to Chaoshan area), Wuyi Yan Cha (I have heard that at one point, this was considered the best, but not sure if it's common now). I'm sure pu'er is also consumed in this area, but whether it's brewed in the same way or not, or whether it's considered gongfu cha, I am not sure.
4) In most ceremonies I've seen, there are either 3 or 4 cups, which should be brewed equal strength... the pot or gaiwan is poured directly into the cups in a circular motion, and only 4 (or 5 at most) brews are consumed. If there are more people than cups, people alternate or defer to each other.
I know you read it, ABx, but for the archives, also worth reading is the bit about the "4 treasures" at http://www.teadrunk.org/viewtopic.php?pid=251#p251
I would assume that almost any type of gongfu cha (and in fact most types of serious tea brewing of any sort) would involve washing / preheating everything, though maybe not before every infusion or in the exact same way.
I think most other gongfu traditions are just variations on Chaozhou gongfu -- adding the cha hai and / or aroma cups (both Taiwanese inventions?), using slightly larger pots / cups, different styles of trays or tea boats. I'm not sure how significant the poetic descriptions of the whole ceremony are. Most of the areas where it is common are geographically close to that area (other parts of Guangdong, parts of Fujian, Taiwan, Hong Kong), and / or have large overseas communities of people from that area.
Are they used, or were they developed, primarily for certain types of tea?
I think that generally speaking, oolong teas, particular the types I outlined above, are traditional. I know pu'er and other post-fermented teas were very popular in Guangdong, but I don't know if they were brewed this way (until recently) or not. I have, however, heard of red tea called "gong fu red tea" (from Fujian, I believe), and I know that Yixing potters also like to drink a local red tea... I'm not sure where drinking red tea in this style was popular, if at all -- presumably around that same area.