iuguy, a few things. Most important I really don't believe that "it will make no difference to me as my constituency is a safe tory seat, even with all the simulations." Even if it doesn't change who actually wins, implementing AV can send a clear message to your incumbent by (for example) showing that 25% of the constituents actually want the Green candidate to win (rather than just the 5% who actually voted for her under FPTP, knowing their vote would be wasted). That seems important to me -- it changes the slope of the playing field.
For the same reason, I am not skeptical enough to accept that "this isn't genuine electoral reform, this is tinkering around the edges". AV would make a HUGE difference to me, for the simple reason that it would relieve me of the responsibility to lie when I vote (i.e. claiming that I want the winner to be someone who is actually my second or third choice).
And for those who actually want PR: we are MUCH more likely to get it in our lifetimes if AV wins this referendum than if it loses; in the latter case, the incumbents really will all say "so that's all right then -- everyone likes how we do it now". Which is so very not true that it makes my guts hurt just to type it.
So even if you think AV is only a small step (and for the record I think it's a big one), please vote for it. It is (among other things) a stepping stone to a more comprehensive referendum on voting systems, similar to the one they had in New Zealand -- see http://www.fastchicken.co.nz/2011/05/05/the-uk-gets-to-decid...