This is being typed on a Lenovo ThinkPad SL510.
Generally I've avoided Dells, usually I hear horror stories from people, same for Acers. I do not know anything specific to the model you've picked out. So I personally would side towards the ThinkPads, but obviously, my view is a little one sided.
In terms of durability and quality of build, I would say you're looking at very well built laptops with a ThinkPad, there's different ranges of ThinkPads, ranging from the value stuff like my SL510 to top quality T Series and W series.
The main features of ThinkPads I would look out for are:
Lenovo Enhanced Experience. This boosts load times on Windows 7 (I think it's version 3.0 in new builds now) I have version 1.0 on mine and I can still pretty much boot Firefox seconds after Windows 7 has booted. I've had the laptop for nearly 2 years.
Rapid Boot Drive. Uses a SSD to boost boot times. My model doesn't have this.
Rollcage Technology. Not every model has this. This is the technology that gives ThinkPads their reputation, basically it makes their laptops extremely durable.
Active Protection System It detects knocks, drops and bumps and it immediate freezes the hard drive to stop it from sustaining damage.
Shock Mounted HDD Essentially your hard drive has shock absorbs, to prevent damage to your HDD.
Spill resistant keyboard I guess handy just in case.
And of course the screens use steel hinges to add durablility. The rollcage is made of a strong but light allow which holds all of the laptop's tightly together and securely.
Not all ThinkPads have the same durability features. Cheaper ranges have some cutbacks. My SL510 for example has the Active Protection System, the Spill resistent keyboard but lacks the rollcage.
The ThinkPad Edge series (the series you're looking at), they are cheaper ThinkPads, they're like mine, but are meant to be more stylish (and are a newer range). They're a good value for what you're getting. I almost bought an Edge myself. I suspect the Edge, like the SL series, lack the impressive rollcage stuff, but regardless ThinkPads are very well built and would likely have similar features to my SL510. I have actually dropped my laptop a few times and it's done just fine - I've not tried stress testing it though (I don't tempt fate) - plus I know it won't be as durable as a T-Series.
With a Lenovo though, you are paying extra for its durability features. I bought mine because I was buying for reliability and not spec. I think if you're going for a business laptop, it is attractive, because you want to keep your data safe, your hard drive in tact and of course should you drop your laptop, you'll need it to boot...and preferably, quickly.

I'd personally argue they earn the extra cost for equivalent spec, naturally that always depends on what a person is looking for an consider valuable.
However, I am very happy with my purchase, I've not had a singe problem with my laptop since I've bought it. I've found it reliable, it's ran nice and cool (and it's pretty quiet, I rarely hear the fan) and it does the job and Windows 7 performs well and the enhanced experience no doubt helps.