All those fancy features like Resume eat your RAM. You can't get cool new features without sacrificing hardware. I wouldn't expect Lion to get much better in terms of memory management. It has been designed to use more RAM than SL. OTOH, 8GB is quickly becoming the norm and $40 shouldn't be too much anyway.
Sure you can, you just have to manage the memory correctly. I am not using all the new features as it is and other things were removed. The kernel task has a habit of taking memory and not letting go when it is finished.
You don't have to use them in order for them to eat your RAM. For example Resume works in the background. You quit an app but it saves the session and will continue from that when you open it for the next time. That takes RAM. Safari 5.1 is also a RAM hog, it easily are over 2GB of my 4GB.
It can sure be improved but people who expect SL-like memory usage are not thinking clearly.