Yeah, the thing about Georgetown is the undergrad students are willing to pay a lot to live in the townhouses because they're still probably paying less than they would on campus...... and their parents are probably paying. There's also no metro, but buses to the metro are easy. Unfortunately, busing to the metro, taking a long metro ride, then busing to WCL seems excessive.
Ouch. That sounded like a mild zinger... to be fair while most Georgetown kids are on the parental dole, I know plenty of people (including two roommates and myself) who pay for their rent by themselves, mostly through part-time work or summer earnings. But that's not really relevant to the conversation.
If you are living in Georgetown, you will most likely NOT be taking the Metro to WCL - taking the 30s to Tenley takes about 15-20 minutes, and you can just hop on the WCL shuttle. Just need access to Wisconsin Ave.
Still, if you're planning on going to WCL, I wouldn't advise living in Georgetown. It's expensive, and just because you're paying more doesn't necessarily mean living standards are any better. If you're in a shared living arrangement, you're probably better off living near Friendship Heights/Tenleytown/Spring Valley/Van Ness - the houses are just as good (if not better) and available for a lower price. Commuting in from Bethesda also wouldn't be bad.
Chinatown is a neat place. I like it - though the Red Line tends to get messy during rush hour. Lots of nightlife, great restaurants (somewhat overpriced) - and the Verizon Center to boot. Not to mention, all of the DC-NYC Chinatown buses are right up your alleys (... literally).
Living in Rosslyn isn't that terrible commute-wise - it takes about 30-35 minutes to get to Tenleytown (10-15 to get to Metro Center, 15 to get to Tenleytown via Red Line, and 5 for waiting for trains/trying to get through the red line crush at Metro Center, especially during Rush Hour). Like Elliga mentioned it is very close to Georgetown (just a long, bridge walk away) - and can be a nice little bit of suburbia while still having access to most of D.C. The only thing - like Georgetown - Rosslyn is almost prohibitively expensive, especially with the new developments going up and the commercialization of the whole area. Friends living there are paying an arm and a leg. If you're considering VA, I would stay in Arlington - and stay as close to the Metro as possible. If you're living in Courthouse and planning on attending WCL - you're probably looking at an hour commute with one Xfer - (40 minutes if you're really quick and can catch your connecting trains - which there's no guarantee...) - and that's not including shuttle time/time spent walking to the Metro.
If you're planning on living a line other than the Red Line - (and people may disagree with me on this) - it's better off to live on the Blue/Orange lines rather than the Green/Yellow. Only because in my experience Blue/Orange line trains operate more frequently at regularly paced intervals. I've had to wait for a Yellow line train (during Rush Hour) for a good 7-8 minutes sometimes - whereas Blue/Orange usually run every 1-3 minutes during peak hours. Again, this is my personal experience, and I'm sure someone else living in D.C. can tell you something entirely different.
Like others have said - Adams Morgan can be hit or miss in terms of safety (it's safe for the most part, but there are some incidents). Woodley/Dupont are fine. I don't really know about Mount Pleasant - haven't been there often enough to personally comment, but friends of mine who live near Columbia Heights/Petworth have both pros and cons about the neighborhoods, and concerns about safety do come up. If you are looking at that area though, you have to weigh the cost benefit of living in Columbia Heights (apartments are cheap for the most part - so are group homes) versus some of the major concerns over the neighborhood (it's an area in transition, D.C. IS a large city, etc.)