There are hardware issues with both shielding the cable and, even more importantly, the length of the cable, vis a vis signal strength and integrity.  Given that, I used the nVidia QuadroPlex recently which is a high end version of what you are talking about, and I just saw this article on Guru3d about another vendor's external graphics card product.

http://www.guru3d.com/news/amilo-sa3650-with-graphics-booster-review/

hmmmm....

The the required technology for external video cards has only become available recently. AGP doesn't allow long cable lengths, so is unsuitabke for external video cards. With PCI Express it has become possible, however, 16 PCI Express lanes is something not many vendors would like to waste on an external port.

There are a few of them out there - I've seen them.  But I don't know why they aren't more prevalent.

Bandwidth.

A 16x PCIe slot is capable of 4 GB/s in each direction. Your average USB 2.0 port is capable of 60 MB/s. Gigabit Ethernet is capable of 125 MB/s (theoretical). eSATA is capable of 375 MB/s (theoretical). None come close to PCIe's max speed.

NOTE: GB/s = gigabyte/s Multiply by 8 to get gigabit/s.

For best operation, a video card needs the full bandwidth of the bus.

The best way to get great video on a laptop is to buy a laptop with great video. Buy a gaming laptop.

I also know some of the older docking stations had card slots built in. It was older tech though (PCI maybe?). Most of what I see now are port replicators. I'm guessing there might be a newer version out there but I haven't looked.

Not with windows XP or above, the HAL eliminates that problem, it might take a minute for it to catch up to you, but the transition is smooth, I took a OS course at community college and they gave the students hard drive bays, so no matter the system you were on, it was always your files and your configuration.

That's odd, because I have XP, and I've cloned my hard drive to an external as a back-up. I was also hoping that i could boot from it using my mom's computer when i came back home, but all it did was start to boot up, get to the XP loading screen, and then restart.

Did you clone the hard drive while running windows from that hard drive?  XP is a bit pickier, might also be because you were trying to boot from a USB hard drive, when Windows starts to boot, the original install expects to look for the files on a primary IDE hard drive, but when it looks there the files aren't what it expects, when I was in the class the OS was installed to the drive while it was in the bay, if you did a clean install to the USB drive that should work.

Anything that can function on the bandwidth limitations of a USB connection isn't going to be a whole lot faster than what you already have.  Plus it will need power, and be designed with ground loops in mind since you aren't likely to be able to draw enough power from any connector coming from the laptop. 

These things can be designed around, but neither is a trivial task with GPU's drawing so much power and unknown feedback circuitry from the laptop side (You don't want to have a ground loop fry you laptop while trying to play a game). 

These are just things off the top of my head, and I have never designed a video card.  I am sure that those have additional challenges that also preclude this from being a common thing.  I know that I have seen these external video cards before, so they are available if you really need one.

Here is one, but it doesn't include 3D acceleration: http://www.everythingusb.com/iogear_usb_2.0_external_video_card_12787.html

USB/Firewire are too slow for the positively obscene amount of bandwidth that a modern video card uses.

Even when USB 3.0 is out (it will be much, much faster), I doubt there would be a significant improvement over the latest Intel crappy integrated graphics chips.

For just one example, remember that a modern video card has at least 320 mb of RAM, but more likely 512/768/1024 mb.  In the near future, 2gb cards will be out (I mean cards that aren't X2).  Well that's 1 gig of information that needs to be read and written to almost instantaenously if a game will be playable.

You could use system RAM instead but you have to reach a point where you say the improvement (if any) would not be significant over even an intel GMA 950 or so, which is the minimum standard for onboard graphics.

I suppose you could rig up some sort of "GPU port" on the back of a computer which has the necessary interface speed, but then you run into another problem - heat.  Either your external GPU is going to be well-protected and sort of attractive, or it's giong to have copper sticking out all over the place.... and you just know some asshat will use it for a stand for his bottle of butane lighter fluid or something and then Nvidia would be no more.

Next, you've got the problem of the end-user.  People are DUMB.  Really, people are massive idiots.  And presumably, if these video cards are external, the idea is that they will be user-installible.  Someone will accidentally bash it or push it up against a wall too hard or use it as a can opener... they'll get busted, and there's no way a consumer will admit to being dumb enough to have been responsible for damaging their $400 "FATAL1TY X-TREME ASSASSIN Z8000 PRO PREMIUM TURBO SUPERCLOCKED VISTA-READY EDITION", it will have stopped working all on its own.

The less user-servicable parts there are, the better.  Damn people are stupid.

In short, it's technically infeasible and without any practical value even if it were possible.

Looking at some of the tech demos and listening to the talks given by people at the EVE:Online Fanfest it seems to be that you don't shove 1GB of textures in to the card, you'll choke the bus/processor/something.  The RAM is for textures/models/etc but also for processing, running micro applications purely on the GPU that figure out shadows, do real time lighting calculations and such.  At least that's the impression I'm getting from Nvidia's Cuda technology and whatever ATI's version of it is/will be.

Curiosity has the better of me, I keep seeing all this well... overpriced tat with FATL1TY written on it.  What the hell is all that about and why they hell can't these people spell better than me?