It really depends for me. If I need something network related, I usually buy local. Unless it's cisco it usually doesn't work the way I want. But yeah the price difference is so big nowadays that I order pretty much everything online unless I REALLY need it right now or I feel like driving an hour to microcenter.
I buy almost all computer parts from on-line. Only exception is I need NOW and that is normally lower cost items. Laptops, I am alittle apprehensive - UPS are not known for being gentle and local is better about returns ie dead pixels. Previouse two were bought at Bustbuy. However the last laptop (a Samsung RF711-S01) I ordered off of newegg - Local was about $250 more so took a chance. Local competition has cut way back from the mid to late 90's. Use to have computer shows at convention centers, ComUSA, Circuit city, and Egghead. Large screen TVs I still prefer local even at the higher price.
Newegg orginally was a brick&mortor store called egghead.
When I am looking at what to buy online vs local, I look at two things. Shipping cost and availability. Online usually means paying shipping which can significantly increase the total paid. However, local very often means poor selection and I always want the best parts. The choices available online are much better which often means the shipping is worth it to me. I usually end up going online just because of the availability. The only time I go local is if I can get the same parts at an equal or better price without the sales tax eating up my savings.
In my case, locally isn't much of an option because I have very little choice available. I don't locally because the available choices are next to nothing, I have but 20 motherboards, maybe 10 different CPUs, 30 varieties of RAM, and the like. Online, with just one store, this gets multiplied by a dozen (or maybe 2 dozen) so I can really fine tune things. Multiple stores expand this out still more. For things where vision is key, such as screens and displays, going there and seeing it first hand is the best route.
There are 3 downsides to ordering online: payment, shipping, and returns. Ordering online requires that you have either a credit card or debit card and you must have a bank account. Paypal also works, for places that accept it (though a bank account is still needed). The worst part about the payment is if the server gets hacked into - your card number can get stolen this way. Fortunately, this is rare. No server is immune to hacking. Locally, you can just bring cash or pay by check (if the place accepts checks).
The second downside is that, instead of waiting only an hour or so to go there, get the item, and come back, you have to wait days or even a week for your item to get shipped. Ordering online is recommended if you don't need the item otherwise right this second. If you can wait 5 or 6 days (3 or 4 if not over annoying weekends), then ordering online is often the way to go.
The third downside is that not all return policies are friendly. Waiting 5 days is bad enough, but waiting an extra 8 or 9 days because of a defective item can really be trouble some. Not only that, but, should the item be heavy, you're stuck with having to pay a considerable shipping fee. I would think that online retailers should refund the return shipping if and only if the item is proven to be defective (and not from user mishandling and the such).
A neutral aspect comes with small items. A 6-foot USB cable, for example, may only go for $3 on a retailer, but you pay twice that in shipping. You're often better off buying such cables and other cheap items locally.
The only weak point with ordering online is groceries - they are often very restrictive as to where they can ship, even for nonperishable goods (technically, everything will perish, but 3 days versus 2 years is a big difference). I'd order my groceries online if I could.
Ha! Ha! Love the comment about groceries especially 'cuz I used to actually do that!!
When I lived in California, there was a grocery store that provided on-line shopping for all of my groceries. I could get everything from apples, oranges and avacados to fresh meat, frozen dinners and canned veggies; literally anything you can get at a grocery store. All of it was shopped for by the local store and delivered to my house within 1 hour of a time that I selected. I could sometimes get several hundred dollars in groceries delivered to my house on the same day. Not kidding one bit! Don't knock it!! It's all true.