qTip is a really nice plugin to use in wordpress, but once you install it in a latest version of wordpress you might get the following error
f(this).data("qtip") is null
This has to do with qTip not being able to work right with latest jQuery versions.
The solution to the above was to manually edit the file jquery.qtip-1.0.0-rc3.min.js
Find the following line:
if(typeof f(this).data("qtip")=="object")
and change it to:
if(typeof f(this).data("qtip")==="object" && f(this).data("qtip"))
Thanks to simshaun that found the solution here: http://craigsworks.com/projects/forums/thread-solved-qtip-1-0-0rc3-does-not-work-with-latest-jquery-release