I have a JBC CD2BC, Metcal PS-900, Ye old Antex station (I forget the model) and Somewhere in a draw a cousin of the duratool (the model appears under several brand names).
The JBC is awsome but has a price to match! If your making any money from it then it is worth it. For day to day work the Metcal PS-900 will be fine.
The PS-900 doesn't heat up anywhere near as fast as the top of the line Metcal or JBC (my JBC takes approx 2-3 seconds from cold) The 900 takes around 30 seconds.
The biggest difference the Metcal and JBCs have over the basic irons are firstly the tips. The selection of tip types for them is massive compared to the basic irons. My prefered is the knife bit as it gets into small spaces and great for my smt assembly, however if tilted slightly can cover large pads too. The tips can also be changed easily whilst hot on the Metcal and JBC to suit the job at hand (easier on JBC irons). The 900 has the heater built into the handpiece (this is changable for when it needs replacing) the JBC and I believe the higher end Metcal has it built into the tip which makes them more expensive but they heat up faster.
The Second difference is heat build up/retention. The cheaper irons say stuff like 120w or higher etc this is useless vs the PS-900's 60w rating. It is not what you have got it is how you use it. The Metcal and JBC keep there heat so much better and heat the components solder so much more easily. As they heat the solder quicker this allows you to get the solder/desolder job done quicker. Thus making it less likely you will thermally damage the component (cook it). The tough test for a soldering iron is to reflow solder on a large groundplane attached component. Most cheap irons will have massive heat sunk into the the component and groundplane, which lowers the iron temp making it difficult to melt the solder the iron then ramps up the power to heat itself up and generally overshoots the desired temp and cooking the component or damaging the traces.
A little video you find interesting regards above points
http://www.youtube.com/watch?v=g2QMX98Li_E
Ant