No, we use Twitter's awesome oAuth functionality to log you in and to deliver your scheduled tweets.
If you fall out of love with us, you can even get rid of us through Twitter by changing your preferences here.
We do actually! We got that question a lot so we build that recently. You can find it here. Let us know what you think!
No, unlike some other tweet scheduling services we don't and will not ever use your account for spammy commercial stuff! (and neither should you).