I'm often reading stuff on my Mac but then I want to switch to my iPad to read it there. Is there a simple way to copy text or an URL from my Mac to my iPad?
Safari's reading list and iCloud works well to synchronize a list of URL between Macs and iOS devices. The Simplenote app and web app work well to let all your devices keep track of text documents. You only need to pay for the latter if you want enhanced features or avoid the advertisements that are minimal and generally very tasteful.
A free no additional app solution exists If you are using iCloud, you can use the built in Notes Application on the iPhone / iPad and coming soon to Mac OS X via Mountain Lion.
But til then on Lion Notes can be oddly be accessed via the OS X Lion Mail Application Notes function. You can copy paste to Notes and then grab results from whichever platform you wish.
Also try NoteFile for iOS devices and the corresponding widget for Mac. It syncs beautifully between both almost instantly. It's made by junecloud.com