For those of you considering a visit to the UK: British Airways is currently running a fare sale for November 17, 2009 - March 28, 2010 (excluding December 21-23 2009) and March 29 - May 23, 2010. Fares to London from most of the major East Coast airports (DC, Philly, NY, Boston) cost around $600 round-trip. Car rental add-ons on the UK side are almost so cheap that they're free.
Edinburgh is about a 7-hour drive from London, but that drive takes you by Oxford, Stratford, Warwick, the Lake District, and part of Hadrian's Wall (or, on the Eastern route, York, Durham, Northumbrland, and a different part of Hadrian's Wall), so if done leisurely, over a day or two, the drive could be a real treat. Alternately, if you just want to get to Scotland ASAP, Megabus runs cheap (but long) buses to and from Edinburgh, the National Rail can find you train fares, and Easyjet runs cheap flights between London (Gatwick and Stanstead, I think) and Edinburgh.
If you're thinking about a trip to the UK, let us know!