I am not sure if Instapaper has apps for anything other than the iPhone, and I kind of doubt, if that exclusivity exists, that it will last any amount of time.
Instapaper is one of those new 2.0 companies that is web/app based. They provide you a free log in to their website, which by the way, by default, had no password. Past this login you get a bookmarklet, similar to the "readbility" bookmarklet I talked about earlier, which, upon use, allows you to turn any article you are reading into a saved article of sorts.
For example, earlier today I was reading an entry on a blog, it was rather long, and I wasn't going to have time to finish reading it as I was about to head out to go to the dentist.
So, with this combination of app/website, I tapped my instapaper bookmarklet, which takes whatever you are reading, and puts it up in the "cloud". Which, provided you then have the Instapaper app on your iPhone, can sync this content down to your mobile device.
Now, whatever article I was reading, just by tapping one button, is now formatted in nice big text on my iPhone, and I can take with me.
I don't know the size limitation of the file you can put on instapaper, I don't know, for instance if you can put a whole book up there or something, but for now, while I am in the dentists waiting room, I have articles to read instead of the weeks old copies of "Newsweek".
Why don't I use something like Google reader? Well I can, except for those websites that shorten their rss feeds to force clickthroughs. It's another couple steps, who knows how it is going to be formatted, and who knows what kind of connectivity you are going to have.
Which, also by the way, is why I removed the "shortened rss" clickthrough thing for my blog. It annoyed me, so I figured it was probably annoying you.