I have a couple of things to say here:
(1) I am ****** what Apple did to the OS which makes it not work well for HDD since Lion, and I am sad that there are more usage issues with the software than I am used to in Mountain Lion.
(2) However, the overall experience with Mac OS X 10.8, on any computer with 4Gb or more RAM with an SSD is still an oustanding overall experience and nothing else comes even remotely close in my experience.
(3) Your issue with Safari using 5Gb of real memory is not completely horrible because (a) you can always quit and restart Safari, which is to say, it's not down deep in the OS that is causing your problem, just a single app, and (b) you could always try Google Chrome, which uses largely the same rendering engine, but a slightly more aggressive and clever way of releasing memory whenever you close a window without quitting the app entirely.
(4) With 16Gb of RAM and nearly 8Gb completely and utterly free, you should be experiencing zero issues with this scenario you show with your Activity Monitor screenshots anyway.
The thing about Safari and web browsers in general is that it's very easy to build complex websites which use up a lot of RAM in the browser, which cause the browser to grow and grow until you quit the browser or at least close that window. One really REALLY bad website which is very very fancy and uses tons of RAM is - wait for it - icloud.com. So if you are using iCloud in your browser a lot and seeing huge growth of the size of Safari, well, don't use it. If it's another site try to figure out what website it is. Any poorly written site can do this, but very few websites are poorly written AND need/use tons of RAM. But in general, if you close the last Safari window, quit the app. That frees all the memory right then and there.
So, if I were you I would not focus on safari leaking memory because there are options: quit safari when you close the last window OR switch to chrome, which frees memory as you close windows because each window gets its own, separate memory pool to begin with.
To Chitt, I think we should hear some more details from you. Since switching to SSD I have had zero problems, on small MacBook Airs with 4Gb of RAM to my current Retina 13" with 8Gb of RAM. Amazing machines, zero slowdown. So give us more details in case it's something else.
BTW - Apple does care. I have had a problem with Apple Mail and Dreamhost for 2 years since ths release of iOS 4.0. I filed a bug report with Apple just recently and the engineers got back to me and told me how to turn on logging on my iPhone. THen then looked at my 5Mb of logs and got back to me with a serious description of what was wrong with Dreamhost's IMAP servers. I told Dreamhost and they said "This is Apple's problem which started when they released iOS 4.0." I thought about it some more and wrote Apple back and told them that I thought it might still be their problem, why don't they think about what they did back in the iOS 4.0 time frame that changed so we can see what that was? The apple engineers wrote back and said "We know exactly what changed, it was SUCH AND SUCH that changed, which is why I pointed you at SUCH AND SUCH article in the last exchange, and BTW, here's an example of a properly functioning IMAP server." Well, they were right, they gave me the information I needed to find the bug report in the IMAP server Dreamhost was using, and now Dreamhost has committed to fixing the problem (by upgrading their servers). The Apple engineers were very patient and very professional and very polite with me. I am very VERY grateful that they took the time to respond QUICKLY to my bug report and various followups.
Just sayin' ...