With Snow Leopard one chose the number of Spaces before hand (in preferences); in Lion one must create spaces one by one. Are there shortcuts to create & remove Spaces/Desktops?
I'm assuming that your question is just as it reads, that you want to find the fastest way to add/remove Desktops.
By default, Mission Control is invoked by hitting F9.
Spaces are now called Desktops in Lion. I will not comment on that change.
If you hit F9, then moving the cursor over each Desktop should give you an "X" in the upper left corner of that Desktop, allowing you to click on that X and remove the Desktop. I believe you maybe required to remove the highest numbered Desktop first.
You also may run into trouble if you have assigned apps to Desktops, and try to remove the Desktop without first re-assigning the apps.
In that same F9 window, there should appear a translucent square in the upper right corner. It will have a "+" in it, allowing you to add a Desktop.
I believe these are as close to a shortcut as you will find native to the OS. It's not really lot of effort to hit F9, and you are there. I don't know how much faster you could make it without causing problems elsewhere.
I hope this helps.
I haven't found a way to add a desktop via a shortcut, but you can call Mission Control through any way you choose, not just default F9. Open Sys Prefs > Mission Control on the top row. Set your modifier keys, plus whatever you want to you.
As for switching, Control + Arrow lets you slide through each desktop && fullscreen app.
I find switching via keyboard much easier, but creating desktops with a mouse to be prefereable than the old Spaces.