I do my shopping online regularly and mostly these are books. I sometimes order from indiaplaza.
You can easily find the popular books, but if you are looking for a book which is not very common, it gives ambiguous results. However, they give good discounts on various books. Sometimes, they do not have the books but they show the items in stock and once you pay, the order never comes.
Sometimes, there are problem with the prices as well. You should always check the price of the book before adding it to your shopping cart and after adding it, as it sometimes takes the price of other edition of the same book. The customer service is not really upto the mark. You just keep sending email and they never reply. When you call them, they are never able to sort the problem.
Another negative is that they never update the status of the order after it has been shipped. So you never know whether the order in on the way to you or somewhere else. If you are looking to buy books online, go to flipkart.com.