I'd go for a second hand hardtail mountain bike if I were you. It will give you the best riding position for around town and cope with the inevitable potholes etc. If you buy some slicks at the same time you'll be quite surprised what it will do speed wise on tarmac. Make sure you leave enough in your budget for a decent helmet, pump, lock etc.
Agreed dragging a rear shock and associated linkages round on road is a waste of time, and you are far, far better with a decent hardtail than some dodgy full susser...it will climb better for most of the time and need less maintenance. My own bike is a full susser with a Fox shock with ProPedal lockout thingy which more or less eliminates "bob" but it wasn't cheap...and whilst it will cane my mate's Kona hardtail downhill, the Kona just feels loads more responsive to pedal effort uphill unless it gets really gnarly.
As a Cherub sailor you'll probably want to tinker with it, so you could always look at getting an older bike that has a decent frame, fork and hopefully wheels (check very carefully for hairline cracks on the welds, especially if it's ally and looks like it's been ridden hard) and upgrade it if you decide to go off road. Hydraulic disc brakes are superb, make sure your frame will take them if possible, or if you get one with cable brakes it's an easy upgrade (however bear in mind if you are on rim brakes you'll probably need new wheels and hubs too) although I saw a decent set of wheels, discs, calipers and levers second hand for £100 the other day.
eBay is a great source of parts as are some of the other sites around like bikeradar and retrobike.
And enjoy it...I'm loving my biking at the moment, there's 10 of us off to the Dog trail at Cannock tomorrow...can't wait! And here's my bike on Rushup edge, Derbyshire, during the Easter break. And yes, Bontrager Jones tyres are CRAP in snow!!
