Watch the Everyday #2 online guitar lesson by Jeff McErlain from Solo Factory: Chicago Blues

Most blues, jazz, and rock use a swing eighth feel in some way, of course there are exceptions, but if you hear something that sounds jazzy to bluesy to you, you are hearing a swing feel. A shuffle is kind of swing feel as well. On paper these rhythms will just be written as straight eighth notes with a notation usually saying "swing feel" or "swing eighths". A good swing feel is essential and poor swing feels can cost you gigs! "That guy swings like a rust gate" is one of the classic jazz jokes out there, meaning his swing eights aren't happening! I would say, apart from hitting wrong notes, a good feel is the most important element to any player.