I have a Dell Precision Mobile Workstation M6400 that is still going strong (although last summer I did finally have to replace the motherboard). It was knocked off a 4' high ledge onto a asphalt-tiled concrete floor while running and you can't tell it was ever dropped. The thing is a tank - and yes it's heavy but it has a fast chipset. The thing was a beast when it was new. The only reason I haven't upgraded is that newer models have a downgraded screen (1200p to 1080p). I'm hoping the next M6x00 refresh will include a 1440p or better screen. :)
Why I like the Dell Precision Mobile Workstation line:
* Discrete graphics card (they use mobile video chipsets though but that's kind of unavoidable)
* Fast I/O
* Built like a tank
* Excellent screens
* Great full keyboards - for a laptop. I'd prefer mechanical, but no way will a Cherry MX switch fit into a laptop
* multiple hard drive bays (RAID capable although I use it in AHCI mode because I dual boot Windows and Linux)
* Very easy to service and upgrade - no glued-together crap and everything is accessible. I can disassemble it to upgrade a processor and have it back up and running in an hour (upgraded from a Core 2 Duo to a Core Quad Extreme)
* Again, easy to service, so every once in a while I open it up and clear all the dust out of the fans, heat sinks and heat pipes
* no-compromise performance so yes it's heavy
I've had clients who asked about my laptop and switch to these workstation replacement laptops instead of buying desktops any more after seeing my laptop. Their concern was ability to run multiple monitors so I explained displayport to them, and the order them with Quadro video cards for CAD.
Oh and as far as enterprise hardware goes - Dell is pretty okay there. Their documentation is dead wrong on some items (particularly the Perc cards) but if you know LSI controllers you know how to work with them. Dell enterprise support is actually pretty darn good, and don't demand you reinstall Windows for every little problem. Tell them the motherboard died and they'll send someone on site with the replacement part the next day without forcing you to run through their stupid phone script like you would if you had bought an Inspiron... and unlike HP they do not demand you upgrade the firmware on a dead motherboard (???) when discussing the hardware failure.
When it comes to HP I like their chassis and blades but their support folks are generally condescending AND stupid (although I have had very good experiences with HP as well, to be fair but the good techs with them is like panning for gold - you get a lot of crap with a nodes on rare occasion) with most reading from a script. I never encounter that with Dell enterprise support; they're always interactive AND friendly.
Oh.... and HP laptops are crap. I don't like Lenovo either because it is difficult to order replacement parts through their web site, but when it comes to Dell it is almost always very easy to order replacement parts - and if a part replacement is obscenely priced they will often offer you a warranty renewal on the product which is much cheaper than the cost of a brand-new replacement board or screen.