I have SBC/AT&T Yahoo! DSL and if I clear all my cookies, I have to redo the login screen for my e-mail. *sigh* No biggie, but usually I just manually clear each cookie.
Regardless, clearing all your cookies won't EVER harm your computer
! (Some people claim that it can...usually because they are depending on that cookie to track your movements!) If anything, they'll help it run smoother and faster...just might have to put one or two cookies back, which we should all do anyways.
An even better thing to do is to get a program like Ad-Aware SE and
use that to clear all tracking cookies and adware and spyware from your computer.