i just switched to gnome 3 and well... i won't say anything offensive just because that's not what i am here for and i want to give this desktop a try since inevitably this is the future for gnome.
anyway i just wanted some tips from you guys on these subjects:
- quick task switching
It's been a nightmare to switch between applications, i always have to go to the activities thing.
- opening new apps instances
a quick way to start new windows for applications? let's say a terminal, i always find myself using more than one terminal.
- where did the systray go?
i remember with gnome 2 we had this little systray right next to the clock, rhythmbox, kopete, kmess and a lot of applications where minimized there when closed. what happened to that useful thing?

forgive me if i am asking too much here, but so far i feel stressed by this desktop, i hope you guys can help me.

And that isn't very different to going to the little square down the bottom of Gnome2 and clicking on it is it. The Activities (or hot corner) "thing" lets you see how many "windows" you have open at once you don't have to go searching they are all there. It's easy to use once you have the swing of it.
Go Hot Corner > Apllications right click on the application you use often and then click "Add to favourites", it will now appear on the "favourites" bar on the left of the screen after you activate the Hot Corner.
If you use Gnome3 properly you don't need that for what you use it for because each application will have its own "window" that only appears when you want to use it. There are applications that will, when minimised (not closed, there is a difference), place themselves in the notification area which is the bottom right corner. Things like Dropbox, Update Manager (for Debian type systems), Skype, and others all locate a place holder there when open and operating.

You can also press the "Window" key on your keyboard (assuming yours is a standard keyboard). This will have the same effect as pointing to the hot corner. I myself use it almost all the time.

If you are using more than one terminal window, try "Guake Terminal". I find it extremely convenient.http://guake.org/downloads