I stand corrected regarding the CO2. Oops!
Your "laptop vs. NJB3" concerns really strike home with me, as that's exactly the situation I face. I'm a software developer, so I always have a pretty new laptop. (Right now I'm on a 1.8 P4 Sony w/16.1 display.) And, I generally have a few of my past units around, too. So when I first started thinking about recording, I figured the best thing to do would be to leverage those assets.
I guess it depends a lot on the budget. The tricky thing (in my brief experience) about putting together a recording rig is that often the "accessories" add up to a significant cost of the rig. So, when you start looking at different equipment routes, the "accessory" cost can be an issue.
For example, I considered the following: (I already had some low-end-but-decent mics from my live sound PA rig.)
1. Laptop (Preamp > Converter > Digital Interface Card > Laptop)
This route looked pretty cool, as the AD-20 or UA-5 handles the preamp/converter in the $300-$350 range. There was some difference there, too. The UA-5 looked cheaper at first, but when you add the standalone mod and a battery, it's more expensive. (Though many here say it's worth the difference!) Interface cards are in the $100-$200 range. I have a laptop. Total estimated system cost: $400 - $550.
But then you have to think about power. By the time you pick up a battery to run the laptop for 3 hours, you're looking at another $200-$500. Ouch.
2. NJB3 (Preamp > Converter > NJB3)
So you're out, say, $250 for the NJB3 and $300 for an AD-20. Same initial system cost as the laptop rig.
BUT -- no battery issues. You've got LIon in the NJB3, and the AD-20 runs damn near forever off a 9v.
So, for starters, you're $200-$500 less. The kicker for me was that I also didn't have to take my nice (or even not-so-nice) laptop into smoky bars/venues and have it smell like a wet ashtray the way everything else I've ever carried in does.
Really, though, since you're talking about patching only, maybe the laptop would be great. There was a guy at the Dallas moe. show who brought his laptop with an interface card. He ended up patched off one of the nice rigs on either side of me (either Drew's ADK TL > UA-5 or Wayne's 4-mic Earthworks mix). I bet he got a better outcome than me.
I guess a lot of my thinking was alse centered around making sure that I didn't spend too much on something until I know it was really for me.
So much for that. It's definitely for me. I love listening to the few shows I've recorded so far, and I can't wait for the next one. Who knows.
In the end, though, I'm learning that it's not what your gear is, but the fact that you're there, and (hopefully) the fact that you enjoy listening to your recordings.
Chuck