I'm very surprised that people don't understand how mac os x uses ram.
The OS will fill the RAM as quickly as possible. Every program you open and most of the cache data inside the app will fill the ram too. Spotlight will fill your ram, your photos will go into ram if you use iphoto, your mail, docs, back up docs, program data, web pages - including text and graphics, browsing history, basically anything you can think off will end up in ram.
All open applications will stay in active ram. Closed applications in SL will go into inactive ram and the program data will be wiped from RAM or possibly stored on the HDD until you power down when all will be wiped. However, in Lion, the resume function holds everything and restores it back into active RAM after power up. That is why Lion uses more.
So, even if you closed a program it will still sit in inactive ram. It is perfectly normal to swap out occasionally. There maybe overages or old inactive RAM that can be transferred to the disk to let currently running programs use the active RAM. The benchmark is to make sure you have < 20% page outs compared to page ins. In the screen shot a few posts above that is the case, running at 14%. That is healthy.
The only time you will run into problems in general operation is if you have lots of programs currently open and you try and do something that needs a bit of ram, or, if you have a dodgy extension in one of your browsers, or spotlight is running, indexing your files. You can solve it by closing some programs.
In the rare instance where all programs have been closed and you still have issues then check for rogue processes / memory leaks or you are trying to do something that genuinely does require a lot of ram. This is very common if you are running SL/L with 4gb and trying to run virtual machines or do video/audio editing. OS X will try to keep any file processing in RAM for as long as possible and if large or after many edits of different files it will fill up and go to disk but this is completely normal and SSD is miles faster than HDD anyway.
You have got to think, OS X is very unlike other OS's. It will fill up the ram as quickly as possible aiming to operate fully from RAM, occasionally swapping onto the disk for old inactive programs. Linux comes close but doesn't pile as much into ram. The way OS X works makes it much quicker to operate. Get used to seeing RAM maxed out and understand that GPU ram is allocated too. Don't freak out when you see page outs. This is more than likely old inactive stuff being transferred to disk and providing it is < 20% of page ins you have plenty of ram. More is always nice but the wired ram is all that is needed by the OS to operate. The rest is OS X caching data making your OS experience faster.