Here we have "a simple tool to save web pages for reading later" which is pretty much it in a nutshell. It's a simple matter to tag a page using a special bookmark script and the page is saved to your Instapaper folder.
|Instapaper main screen|
I haven't tested this feature but you can also download text versions of the pages in epub or mobi format - I guess if you'd like to collect some articles to read on your e-reader device.
All-in-all it has proven to be of huge value to me and I use it daily. Give it a try.