WordPress.org

Where can I change the options?

Go to Settings > FB I Like Button.

How can I force the I Like Button to appear/disappear in individual posts and pages?

You can overide the settings as per page/post by typing the following code in your post/page: <!--fbilike--> if you wish to display the button or <!--nofbilike--> if you wish to hide it.

How can I position the button to left/right relative to content?

Use the option Container Style and style the div around the iframe. Eg. if you want to position the button to the right write something like float:right; margin:0px;. But pay attention not to mess other elements and their position. Use clear:top,bottom, left carefully.

Should I use XFBML?

The default option is the iframe. XFBML was recently launched. However I recommend XFBML because is more handy, fully asynchrone and will offer more features in the future.