[Nook Color General] Blue6IX:
Check my sig for the links to see what the deal is.

Basically, class 2 or 4 SanDisk is what you want, 8 gig minimum, with better performance gains the higher the capacity of card. 16 gig performs better then 8, and 32 better then 16.

The reason is the level of attention manufacturers pay to small block read/write data pathways physically inside the card itself. Running android from the sdcard doesn't matter so much about large-block file transfer, it's all the small writes to and from memory that are important.

That kinda ties in with what I was gonna say to the OP, though, consider this:

I just bought my lady a Nook Color for her birthday, and set it up with the latest stable cm7 (7.1.0) and had it set to the internal memory. I figured, what the heck...she's not gonna do anything else with it.

Wrong move. Putting the finishing touches on it the night before I her birthday, I saw a problem with the screen, I pressed the app drawer icon and a wave of liquid flowed halfway across the screen. As the night wore on over the next hour or so, it got worse and started to become unresponsive.

Obvious hardware failure.

I spent the rest of the night setting up one of my good SanDisk memory cards with her installation on it, and wrote everything (pictures, icons, etc...) to the memory card and nothing to internal memory.

Now she has all her apps, custom icons I made for her, boot screens, albums of pictures from the time we spent together and so forth all on the MicroSd card.

When B&N opened the morning of her birthday, I took it back and exchanged it for a new one. Popped the memory card in, and it was good to go.

Now if her Nook Color ever fails her again (which is very infrequent, was just a bad one out of the factory) all she has to do is pop out her memory card and put it in another one, and it's like nothing ever happened.

Using verygreens installer, and the latest release of CM7, it's a seamless, fantastic setup. Honestly, i'll never install to internal memory again. I never did on my Nook Color, and given what happened there I can't see a reason to ever do so again.

From a dev standpoint, leaving the Nook Color stock on emmc has many advantages, and from a user standpoint the same can be said but for different reasons.

To each their own, but I spent a lot of time figuring out how to make it run well from the MicroSD card, and why some things didn't work as well.

The bonus is you don't void your warranty, and the stock Nook Color software will format any MicroSD card you put in it once it's booted, regardless of what the partition table on the card itself is like.

Just my .02 cents, best of luck with the Nook Color for your wife.

Edit to add:

If you do make an sd-card install and restore the emmc to stock, then keep this in mind:

I used to recommend the app "sd speed increase" made by a member here at xda, because it helped considerably with running from the sd-card.

Not anymore. The newest version of cm7 stable incorporates that fix into the build, and trying to run the app over it actually presents a decrease in performance.

CM7.1.0 is pretty optimized for sd-installs, in addition to running fantastically on internal memory (from what I hear anyways, i'll never know!)