I think I'm the only regular poster from Johns Hopkins on here so I'll chime in. The Greek system at JHU is pretty different depending on whether you're NPC, IFC, NPHC or MCGLO.
This is a ridiculously long post. But
in a nutshell, the Greek scene tends to be dominated by the NPC and IFC groups. MCGLO and NPHC groups are smaller and tend not to be well-known on campus. The NPC groups are very large and pretty social with each other whereas the IFC groups are smaller and more clannish. About 25-30% of the campus is Greek, and those who aren't Greek usually don't care much about those who are. I wouldn't say it's an anti-Greek campus - just indifferent. And they usually won't go to events thrown by Greeks unless they involve alcohol!
If you want (a lot) more detail, read on.
There are currently 3 NPCs, Phi Mu, Alpha Phi and Kappa Kappa Gamma. Kappa Alpha Theta formed from a local in 1997 and was closed for RMF in 2009. Delta Gamma was around from 1990-1995, and I think it closed due to low numbers. There are no locals (at least not any well-known or University-recognized ones...). Both Alpha Phi and Phi Mu were founded in the early 80's and though I've heard Alpha Phi was reorganized once or twice, I can't say whether or not that's 100% correct. Kappa was installed in 1999, and Pi Beta Phi is colonizing this fall. I can tell you from personal experience that new groups have it tough here - even nearly 10 years after our founding, Kappa was still on somewhat shaky ground (doing much better now, though). Alpha Phi, Phi Mu and Theta (which was a local for quite some time before going national) were/are very well-established groups with high numbers, strong alum support and strong presence on campus. Kappa has gotten there, but not without a lot of work. Pi Phi will have a challenge in becoming well-established, but their extension team knows it and I think they'll do just fine. In any event, none of the sororities are housed and they are all pretty large - this spring the largest was 144 and the smallest was 123. There is a lot of crossover in terms of groups of friends, so Panhellenic unity is pretty good except for during Recruitment (where everyone just gets super-competitive) and Greek Week, specifically Powderpuff Football (ditto). There are some big events, but chapters aren't necessarily known for their events since they don't always do the same thing every year. Alpha Phi used to do King of Hearts, but they've done a Casino Night for the last few years. Phi Mu did a very successful Pastathon this year, but I don't think they did it last year. Kappa has done a cook-off and a charity fashion show in the past. All in all, the groups all have fantastic women in them and a lot of pride. Every group has their own lettered tote bag and you see them all over campus!
IFC fraternities differ in a few big ways: there are much more of them (11), they're smaller (last spring the smallest was 13 and the largest was 104, with most around 50) and they're housed. The University doesn't provide housing, and most of them have row houses that 5 or 6 brothers rent and live in, but the whole fraternity uses. Alpha Delta Phi and Pi Kappa Alpha, two of the largest groups, have small apartment buildings that they exclusively rent which house the whole chapter. Sigma Phi Epsilon and Sigma Alpha Epsilon have their own large houses that usually don't house everyone, but fit many of the brothers. My gut feeling is that the fraternities are more clannish than the sororities due to these three factors. There is some crossover in terms of groups of friends, but it's much more of a sense of once you rush, these are your brothers and this is where you go to hang out. Most of them do not have a big signature event, but there are some - FIJI Islander, Phi Psi Beach Party and SAE Paddy Murphy come to mind.
To be honest, I don't know a ton about the NPHC scene. A lot of NPC/IFC greeks don't even know there is one, which is unfortunate. The Alpha Kappa Alpha and Delta Sigma Theta city-wide chapters recruit at JHU but they're not recognized by the Office of Greek Life because they include non-JHU students and there are insurance issues(?). The Office does recognize a chapter of Sigma Gamma Rho and Alpha Phi Alpha, but they're small - 6 and 3 members last spring, respectively. There really aren't any events where the NPHC community and the rest of the Greek community come together. They really tend to do their own thing. A friend of mine in APhiA told me about step shows and events his chapter was involved with, and they were all Baltimore city-wide events or at other schools, like University of Maryland.
There are a few Multicultural GLOs and they also tend to do their own thing. They don't participate in formal recruitment - they do their own COB-style recruitment. There is only one fraternity in this category, Iota Nu Delta, which is South-Asian interest and very small (6 members). There are two Asian-interest groups, aKDPhi and SOPi, which are smaller (19 and 6 members last spring, respectively) and tend to be all-Asian and pretty exclusive. The most widely known MCGLO is Delta Xi Phi, which is multicultural-interest and usually has around 15 members. They've had the highest female greek GPA for years now and do a ton of community service. They also participate in Greek Week events (the other MCGLO groups are invited to but don't usually get into it). In general, the MCGLO groups tend to be small and not well-known on campus.
If you have any more questions, PM me!
ETA: I meant to add something about how Johns Hopkins as a school relates to the greeks there. I think the biggest thing is that there's definitely an atmosphere of "work ALWAYS comes first." In the past we've had some well-meaning LCs who had trouble with this - for example, one wanted us to go sit in the cafeteria for hours, wearing our letters, to promote the group. Sisters were pretty incredulous because they had too many other things to do, like research, lab work, studying, jobs, etc. In all the NPC groups here it's very much an attitude of school first, everything else (including my sorority) second. I've seen girls disaffiliate (in all 3 groups on campus) because they felt the sorority was demanding too much of them and it was interfering with their workload. And we don't even have that many required events, for that reason specifically! I don't know how much of all this is typical of greeks at other universities (regardless of US News ranking), but it's definitely something I've noticed here that differs from the attitudes of greeks I've met at some other schools.