I went last year and got myself my Siggy 10-20 from the Jacobs 'stand', about £30 cheaper than my local Manchester Jacobs store, and was able to compare it with 3 or 4 other stores exhibiting, like Jessops, AJ Purdy's and one or two other smaller stores.
I'm being led to believe, given the current 'credit crunch'/exchange rate/price rises situation, that there may not be the same offers this year.
But it depends on your situation, last year I wasn't in a rush for my lens. I knew I was going to Focus so I hung on, with the attitude if I get it a bit cheaper, great, if I don't I'll shop around when I get home.
Pete