Waterstones have a great eBook site, and there are a number of others out there that work from the UK.
IMHO, the Ipad will not make the slightest difference to ebook consumers. It's the pleasure of reading from a natural looking e-ink display that attracted me, not wading around with flashy over-marketed Apple branded hypeware.
That said, my Sony 505 does run out of batteries far faster than I expected, and I am all too frequently disapointed when picking the device up after a few days and finding the battery warning message appearing. My next ebook will definately have genuinely long battery life as it's major feature.