Recently, I got a Kindle Fire for Thanksgiving. I also have a nook Color that I have used for about half a year so far. Both are software hacked, but no hardware modifications yet.
Common advantages:
* Low cost but good performance.
* Android platform is excellent for engineers. Both work great with PIC24FJ64GB002-based "Kelly Wu" ADB board.
* Rubberized back improves grip.
Kindle Fire advantages over nook Color:
* Much faster. No surprise there since it's a dual core CPU as compared to nook's single.
* Audio connector supports microphone. Very good for VoIP and voice recording use.
* Uses 100% standard USB micro cable for data transfer and high speed charging. The nook needs a special cable for high speed charging, but is usable with a standard cable.
* Audio connector on bottom means audio (headphone/microphone) cable is less likely to get in the way and reduces problems with dust causing connection problems. However, an oversized cable can interfere with connecting USB at the same time since the connectors are very close together.
nook Color advantages over Kindle Fire:
* Runs Cyanogenmod now. More standard Android apps run properly.
* Supports USB host for external keyboard with adapter. Kindle might also be capable of it, but no info yet.
* Supports Bluetooth with hack. However, based on a teardown, the Kindle is likely also capable of this.
* App available to "force" high speed (1.8A) charging as long as special USB cable is used. Should also be possible with Kindle, but such an app is not yet available for it. A hardware adapter works nicely, but is another item to carry.
* Has microSD card slot. Apart from more storage, the fact that it can boot from it makes it very difficult to "brick" it.
* Slightly better battery life in real world use.
Common disadvantages:
* No HDMI output. The OMAP chipsets in both are capable of it. Such a capability would be very useful for presentation and video playback use.
* No official support for external keyboard. USB host hack on nook often needs several tries to recognize keyboard.
* No fold out stand. Needs external stand for hands-free benchtop use.
* No digital audio (S/PDIF) output. Not unexpected as neither device was designed for use as a music player.
* No USB networking (Ethernet emulation) support. Only a software limitation and can be overcome if a developer wanted that feature.
Conclusion: As expected, the Kindle Fire looks like the new best $200 tablet for engineers. Most of its disadvantages are due to software and should be solvable. (Beware that the new nook Tablet has a locked bootloader, which currently disqualifies it from being a good tablet for an engineer.)