Dude, have a look here too: http://wiki.maemo.org/Swappolube

I've been using no OC, just a few scripts to speed up the N900. No power kernel, just the stock one and swappolube, CSSU also installed.

I can have quite a few browser windows open and the phone is still quite responsive and very usable, much better choice to speed up the N900 than OC, in my opinion.

---

Having all the memory used is not a bad thing, it's called memory management. Look that up as well