For the <1% of people who run three screens this is very important. For the remaining >99% it is unimportant unless you are an AMD fanboy and just like extra features that are rarely used.
Given a choice out of having multi monitor support, or saving £1, I prefer to have that pound.
3 screen support from one GPU was pointless until now really.
Earlier, one card with three screens wouldn't be able to play games that well. However, with the powerhouses we have nowadays, if nvidia didn't have 3 screen support from one card, then they'll be falling behind.
Earlier, they were slightly behind, but that would only be because of fanboys (mostly) of AMD who made eyefinity such a big thing. With the 7970, eyefinity is a proper, recognisable feature as opposed to a gimmick IMO