Yes I do, and I really notice it when using O'Reilly's Safari bookshelf. Whenever you select text it pops up a window asking if you want to highlight or make a note, so irritating! If that mouse is in my hand I always select text that I am reading. I am not sure why. Perhaps it's just a reflex so I can keep track of where I am in the text. With so much noise on web pages, it must help. I'll have to test if I do this as often on other things. I know I have accidentally cut and pasted previous commands in a terminal and have been very upset with the consequences. I'm just sloppy with that mouse and middle button I guess. But those darn new line characters on a paste can be catastrophic.