Placement of logo in a website

Face of a Website
People say that the identity of a website is a Logo, of course otherwise it is hard to determine what site are we viewing.
In real life we have a name and a face so also in website term domain is a name of the site and logo the face of website(People do remember the Face rather than Name) .

Importance of the placement of logo
So people remember face rather than name that itself gives the importance of the placement.

Left-top
Mostly the logo should be on the left-top side of the site, this is because the user's eye will always popup of the left top side(Human by nature are like this).
So the safest way to place a logo on website is on left, but if you would like to have it other way(try to break the common path) then you need to act a bit.

Right-top
When you are placing the logo in the right top then try to keep a bg element or a tab kind of bg so that the logo just emboss on top to give clarity to user about its origin.

Bottom
This has to be avoided , basically you don't know the users browser tabs and the height ,
this will make your logo to hidden below the fold of the browser.

If you are making a fixed height website then you can keep the logo at the bottom.(Ex. flash sites).
But I strongly feel this position of logo has to be avoided.