I enjoy using them when I feel like they're good for the moment. I love the kissy face because it's funny. XD The poo smiley is great, too. I also enjoy the XD smiley with the tears in the eyes.

If we're talking about text, not an image, then I use tonnes of faces on forums and in conversation and stuff. Like XD xD Dx B) x) c: :c xc cx c; C: :C :[ :] :( 8D :B O: :P >:c >:C >:( O:< :3 x3 >:3 :3c and maybe a few others. I do enjoy them for their expressive qualities. xD