Just found this thread and the various links so I thought I'd add a few comments if anyone's interested.
Re: accommodation: Youth hostels are a good option if you don't mind somebody snoring half the night. As a walker, I gave up on hostels a few years ago when I couldn't get into Lulworth Cove one night because it was full of weekending townies who'd bombed down from London in their GTi's and obviously couldn't afford a B&B after paying for the petrol to get there.
Wild camping is certainly possible, especially in the Highlands. Also, if you book a month or so in advance, Travelodge do rooms all over the UK for around £29 or less (some are £9 if you book six months in advance). There are also loads of independent hostels in Scotland (there's a map available from somewhere) which can sometimes work out cheaper than a posh campsite (esp. if you're solo).
Scotland: Have to agree with what others have said - fantastic. I went up to Scotland last April (admittedly in my beat-up old Micra) and broke the back of the journey by bombing up to Kilmarnock Travelodge, then took the CalMac ferries across to the Kintyre and Cowal penisulars and on to Mull and Skye, nicer in my view than sticking to the main Glencoe - Fort William route (loads of photos on Flickr if you're interested). CalMac are great if you phone them for advice about a combined island hopping ticket.
Nearer to home, if I need to travel from Leicester down towards Bath or Bournemouth, I avoid the M-ways and take the B4455 Fosse Way through to Circencester or the A361 to Devizes - both great, generally uncluttered, cross-country routes.
If you're coming up this way, the B6047 Market Harborough to Melton Mowbray got voted best biking road in the country a few years ago by Ride magazine, but take care as it can surprise the unwary. Personally, I preper the B664 up to the Harley dealer in Uppingham, then on to Oakham.
And down sarf, there's a great square of biking country from Salisbury - Shaftesbury - Blandford Forum - Ringwood.