Profile Picture Preview

133px on the profile page is the largest this photo is ever actually shown at, and it still isn't very large — a logo or face that reads clearly at that size can already be close to its limit before shrinking down further to the timeline and reply sizes.

The 32px reply avatar is worth paying particular attention to, since it's the size attached to every reply you post in someone else's thread — a much more frequent touchpoint for most active accounts than the larger profile-page version most design effort tends to go toward.