Memory usage Unity VS Gnome shell

As we now it gnome "shell" and unity is near
Unity = the new interface for Ubuntu 11.04Gnome "shell" = the interface for Linux Mint
None of these interfaces uses "low memory", in fact you can compare them to Windows 7's aero effects.
It uses more or less 500 + MB which isn't bad, most of the new computer's comes with 4 GB + RAM.
So 500 MB is only a small portion. However when you open applications it is sometimes able to move up to 800 MB (depending on the application). 

There are lot's of Interfaces out there:   Xfe, KDE, Gnome, Unity, enlightenment, a new type of mix from gnome 2 and enlightenment (moonOS uses this). 

Xfe being a really small footprint, enlightenment being also rather small and more or less based on Xfe. 
KDE an interface using a lot of memory. Gnome the overall loved and used one. Unity the new guy on the block, which wish to produce an easier interface for "noobs" and a powerful interface for power-user's and geeks. 

Linux was always known for it's fast startup and shutdown speed's and heavy workload compatibilities, but are all of this disappearing?

 I totally have to disagree on the question, for windows still uses more space and more memory, MAC also uses a lot of RAM, but hopes to bring a better release in the next line of MAC OS's, Mac Lion. Linux the free, light, fast and also beautiful OS which doesn't loose the title "FAST" in my opinion. Most computer's run 4 or more GB RAM, some "geeks" and power-users are eager to use there let's there 8 GB of ram, while  the typical "noob" might not care! Others are burning to use the full potential of there computer!