Time for new tires I think.

So, on the way to work this morning I got another flat.  Same wheel as the last two.  No sign of anything sticking out the tyre, but there's a wee cut from the last time, which to be honest is pretty visible.  Not sure if the tyre just flexed, and pinched the tube, causing the flat, but whatever the reason, it's time to change the tyres.

I've been recommended these beasties by Schwalbe, so I think that's the way to go.  The guy I know who's using them has done over 4000 miles on his and not one puncture, so that sounds like the way to go.