Our firm now has four of the previous generation 15" powerbooks (1.67 Ghz, most of the optional bits added) which all have been purchased via the online store. Of the four machines, one had to go back and be replaced (wierd keyboard problem prevented you entering any information... so hard to use!) and the other had to have its motherboard replaced (USB sockets all not working). Not a great hit rate (50% failure seems high...) but Apple were very very responsive and fixed / replaced with no problems or funny business. But we've now got a corporate policy to buy the 3 year support package on all new machines, as in both cases these would have been very expensive failures to fix if they happened outside of warranty period.
Now that we have them all working, all have worked extremely well and are very much liked by their users - all of whom used to have WinXP laptops.
We also have a 12" Powerbook (867Mhz) which has been soundly abused for two and half years (including being dropped down a staircase...). Worked very well (but now getting a bit slow...) but last month the superdrive gave up the ghost: getting it fixed would have been $$$$ so we've purchased a firewire DVD burner for much less and it carries on.
So... purchasing online in UK is OK to do. 15" 1.67Ghz machines very good. But be prepared for first one you get not to work - but if it doesn't Apple should be pretty good to fix it up for you.
