Since I've got the GPRS settings for my Nokia 3650 correct, I was able to use Nitro a bit more extensively. This included using Raissa, SimpleMail, Nethopper and NewtScape. Overall, it went quite smoothly, no crashes and more or less acceptable speed (the 115kbps figure for IrDA is just theoretical, the protocol overhead is quite big).
It seems that at least for me, the combination of a Newton and a cell phone covers most use cases. It is actually strange that the situation has gotten better recently with the rise of RSS. It allows me to fetch information in a compact way, without having to visit huge, feature-laden web sites... but I still have to put together a package with some sample RSS channels.
[if you looking for a tutorial about using Nitro and IC/VC, here it is.]