I would never buy any goods by randomly walking into high street store - I find the 'reserve and collect' option far better as it's the best of both worlds. You get a competitive internet price, but you can go down and check out the product before buying, plus returns are a lot less hassle.
These days between comet, currys and pcworld you can usually get prices to match internet only places like Amazon and Komplett, although Dixons-online is usually the cheapest by a few quid.
Jessops I find to be quite expensive, both in store and online - you don't mind paying a bit more in a specialist shop if the staff really know their stuff, but I've never found that to be the case with Jessops. Plus these days, who needs in-store advice when there's so many web sites with all the answers, full reviews, tech specs and comparisons etc?