I've integrated Facebook's Like Button and Like Box to Wopular's homepage and subpages. I don't think they're effective traffic drivers, but did it just to cover my bases; I think, in general, that's true for most small to medium sized sites. They're pretty easy to integrate. It's really just a matter of creating a Facebook Page (aka Fan Page), sticking the url for for that page into their code generator, and clicking on the "Get Code" button.
If your site doesn't have a light or white background, good luck on making a seamless integration. Other than allowing you to customize the width and height and the content that appears on those widgets, there's not much in terms of look-and-feel.
You can customize the Like Box with a few hours of work, but it seems to only work in FireFox, so why bother (when most people are still using IE).
REFERENCE:
Like Button
http://developers.facebook.com/docs/reference/plugins/like
The official page from Facebook
Adding Facebook 'Like' Buttons to Your Site Is Damn Easy
http://www.webmonkey.com/2010/04/adding-facebook-like-buttons-to-your-si...
Step-by-step instructions from WebMonkey
Adding the Facebook Like Button
http://www.facebook.com/note.php?note_id=394114406695
Step-by-step instructions for TypePad users, but is good info nonetheless
How can I create a "like" button for my Facebook fan page?
http://www.askdavetaylor.com/make_create_like_button_facebook_fan_page.h...
Has a widget that can create Like buttons for you Facebook page
How to Add a Custom Facebook Like Box to Your Site
http://line25.com/tutorials/how-to-add-a-custom-facebook-like-box-to-you...
How to Customize your Facebook Fan Box
http://www.daddydesign.com/wordpress/how-to-customize-your-facebook-fan-...
This is the older version, when the Like Box is know as the Fan Box
