Delivery times are the worst bugabear to me.. I KNOW when I order something on line what the shipping costs are & I can make decisions as to whether I am willing to pay them or not !... Often you cannot be sure how long it will take before it is delivered. The worst habit some sites have is to take your order for something tat appears to be available AND only after taking your order ( and sometimes cash) do they tell you it is "on order". The worst offenders are also difficult to get a refund from !
To give you some perspective of this poll read this blog:
Can't someone please fix online shipping, already?
Aside from trustworthiness, prices, and customer service, what's the most important factor when it comes to choosing e-commerce sites?
-- Shipping and handling cost (Please explain.)
-- Options as to shipping carrier (Why?)
-- Delivery time (What's your expectation?)
-- Return policy (What's your expectation?)
-- Other (What is it?)

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic