Andrew,
As Mike says, the pickups which Gordon regularly uses on his guitars are the Fishman Rare Earth Blend pickups with a built in microphone on a goose-neck so that they can be placed at an optimum point in the soundbox for a good sound (whatever that animal is).
Now here's my personal controversial comment... there is a lot said about the only
proper way to capture the sound of an acoustic being a good external condenser mike - and in the studio, absolutely. However, in the hurley burley world of live performance a good pickup is a really practical compromise. So long as it's one that produces a good, usable live sound. Life is full of compromises and playing live, doubly so.
I've certainly found that a pickup/mike blend system is a great way to get a sufficiently authentic sound live on my two acoustics. On my Fylde I've got a Fishman which is pretty much GG's set up. On my Brook I have a different system - the LR Baggs Dual Source which gives you an under-saddle piezo pickup and an internal PZM mike which can be fastened to the back of the guitar or the soundboard...
Both systems work really well and give you a degree of control over the system onboard without having to cut or drill holes in the guitar. Many people are sniffy about just the magnetic or undersaddle pickups but in my experience (particularly in a band mix rather than solo) the produce a surprisingly servicable sound on their own. Certainly the sounds are a
little bit more synthetic than true acoustic sounds but no worse that any other good pickup system. Again... particularly where the guitar is part of a larger mix of instruments. I've heard some say how the Fishman magnetic pickup sounds rubbish and just like slapping some rubbish electric guitar pickup on there (nightmares of '60s and early '70s add on pickups will be flooding back for some of our members!). That's just not true. Acoustic pickup design has come on leaps and bounds over the last 20 years - and Mike Vanden who designed the pickups the Fishman is based on is a genius!
Of course the fun starts when you start to blend more of the mike into the sound mix and this really does make the sound come alive. You do get a lot more depth to the sound and the sound does seem more "airy" and rich. So why not just go 100% mike and forget the pickups? It's compromise again. As you increase the level of mike vs pickup the feedback threshold of the guitar comes down massively and can become difficult to control. My Brook is a very resonant guitar and, frankly, 50/50 or 60/40 (piezo/mike) gives a great, natural amplified sound so there's need to push the mike to higher levels.
Anyway, summing up, the headline is that a pickup/blend system will tend to give you more flexibility and scope to get a natural sound than just a magnetic or undersaddle system alone without the difficulties of being stuck stationary in front of a mike stand, terrified of moving in case the sound of the guitar suddenly drops out as you move away or explodes into feedback as the mike strays across the sound hole...
But I'm a bass player... what to I know?
Trevor