well... to be honest, i just got me zendstudio. as in, i havent had a cj=hance to install it yet. being im fighting with a new linux install.
but from what ive read. its more than just a syntax hightlighter. it remembers variables, functions, class methods all sorts of things.
as you start to type a function (even one you've defined) it will bring up hints on the arguments for said function.
it has mysql database intergration built right in. the list goes on.