I felt this in several cars that I test drove. From what I have read, it is the throw out bearing and is common in these cars because of the cheap plastic throw out bearing that BMW uses. I wouldn't let it scare you off as you will probably encounter it again and from what I have read it does not lead to anything worse with the clutch, just the annoyance of feeling that vibration like feedback in the pedal.
Someone with better clutch/trans knowledge might be able to add to this...