To get the icon back, double-click on your Macintosh HD and go to the "Users" folder. Then drag your "home folder" back to the sidebar.
Trivial Pursuit time!
Here's something that I think the average user doesn't know about:
You don't have to be "outside" a folder to add it to the Sidebar, Dock, and so on!
You can
drag the icon in the title bar to the Finder Sidebar or to the Dock.
What you do is you bring your mouse over the folder icon in the title bar.
Click-and-hold it for a sec; the icon should turn gray.
Then you can drag it to the Finder Sidebar or to the Dock (right of the separator).
Furthermore, this can also be used to
move the folder! (or
copy by holding Option and drag)
Yes that's right! Move the folder (even to the Trash) while you're
in it!
Neat, eh?
BTW you can also drag things (folders, home, pictures, etc.) up to the bar just below the title bar so they're always available up there too. Just take whatever folder you want to put there and drag it up next to the little spotlight thing and wait a moment. You can drop it there and it'll show up on any Finder window you open.
You can't drag them off though, you need to right [control] click the icon and select 'Remove item'. Might be a good way to prevent accidental drag/poof-age.
Like any Toolbar item,
you can drag them left and right or "poof-drag" them by holding Command then drag.