I just got a Kindle, and the send-to-kindle applications look very appealing. I'm wondering about the legality of these read-it-later services. I know that some websites have terms saying that the content on their websites cannot be accessed by any other means than those provided by the website—is the fact that Amazon and other companies download content from third-party websites to serve to us illegal?
If you use the "Send to Kindle" program/browser extension, you have already accessed the content from the remote website. You are simply sending the (already downloaded to your PC) data to Amazon, to have it available on your Kindle devices.
The Terms of Service are here: http://www.amazon.com/gp/help/customer/display.html/ref=hp_bc_nav?ie=UTF8&nodeId=201238330
A different legal scenario is when a site owner incorporates the "Send to Kindle" button in her or his Web site. In that case, they accept these ToS: http://www.amazon.com/gp/help/customer/display.html?&nodeId=201139380?ref_=stk_wdg
Other similar services like Pocket have similar ToS.