Not a real ATCO but I can claim a bit of knowledge about ATM Systems.
The discussion on Mode S has strayed a little from the original question. The Track Data Block (TDB) is the small block of text associated with an aircraft's target on the radar display. The TDB contains information about the flight some of which it gets from the radar responses and some which it gets from the flight plan. With Mode A/C the radar response gives us position, height/altitude and its Mode A identification. Using the Mode A we can add callsign and destination from the flight plan. With enhanced Mode S the aircraft will downlink a lot of additional data some of which can be displayed on the TDB. With most modern systems the TDB can be moved around the target and the ATCO will have some choice over the amount of information included. The TDB is always a compromise between giving the controllers the information they want and their contradictory wish to have an uncluttered display.
Although this extra information is very useful and is the visible advantage of Mode S for most controllers there are other advantages of Mode S which are probably more important. First, as others have said, Mode S uses selective addressing of aircraft transponders. This reduces considerably the problems of garbling, which happens when replies from two or more aircraft arrive at the ground receiver at the same time, and unwanted replies to other ground stations which have to be filtered out. The reduction in garbling means radar can be used in the stacks where previously it was too unreliable which in turn allows the use of safety tools like the Vertical Stack List which just wouldn't work properly with Mode A/C. Second it overcomes the problem of there not being enough Mode A codes to go round in some parts of Europe at peak times. For backward compatibility the Mode S transponders downlink the selected Mode A code to be used by the current generation of ground systems. Future ground systems will use the flight plan id to do those things the Mode A code is currently used for. The Mode A and Flight Plan Id still have to be entered by the aircraft crew.
The IAA website has some information on NOTA.
How the VORs are used for the stacks is difficult to describe but I find most people can understand this if they look at the STAR plates which have the stacks on them. The STAR plates for both Heathrow and Gatwick are available on line from the AIS site. If you google AIS EGLL and AIS EGKK you'll find them quite easily. You need to look at both because you'll see an obvious difference in the way the stacks are defined.
The iFACTS look ahead time is a function of a number of factors. First the amount of processing the system has to do depends on it so the longer you set it the more powerful your processor has to be. If you set it too short you lose some of the benefit to the controller but beyond a certain point there's no further benefit because you probably don't care about whats going to happen sometime after it leaves your airspace and the further you look ahead the less certainty there is. On our small island it is quite possible that in half an hour an aircraft will be interacting with aircraft which are currently on the ground and with the tolerance we currently have on slot times no system can predict those interactions with any certainty.