I read RSS "offline" on the subway all the time... It's the main reason why I used my 770 and kept the IT long enough to want to upgrade to the N800.

If you do a RSS Reader refresh, you will cache all of the newest items (and sadly only the newest -- grr) locally, but *only * the RSS items. If you read a lot of full-content feeds (like Engadget) this works pretty well. But yes, it won't fetch the linked page so it's not great for reading the NYTimes feeds or the CNN feeds where the RSS descriptions are uber-short.

You'll want to switch to offline mode while you're reading them since on the 770 it won't cache images, only text, and that connection dialog will open again and again. On the N800 they did add an image cache which makes it that much better, but if you sync a lot of feeds (like me) you'll see that connection dialog soon enough.

Really, this is what I do 80% of the time on my tablet. Reading RSS on the subway = AOK.