Tbh, I've never really looked through stock recovery options, but I believe it's rather limited and you can only flash authorised ROM's.
Just to expand on that and to satisfy my curiosity, what steps do you need to go through to put a custom ROM on the GN? How does it compare to the steps you go through with other popular android phones?
I only ask because I find the whole custom ROM thing a bit of a ball-ache. My only experience so far was putting CM7 on the HTC Desire and I admit it wasn't something I particularly enjoyed, mainly because of the lack of continuously updated noob-proof guides. The amount of reading I had to do was heavy. This is probably my problem though, I like to understand EVERYTHING rather than just jumping in and getting on with it

I hoped stock ICS would satisfy my needs feature-wise, but it would be nice to know that it’s a painless procedure to load a custom ROM in the future if needed. Is that the case?