Never. But when we were kids, my brother was often taken for a girl. He got the beautiful long eyelashes instead of me (grrrrrr), big blue eyes (again, grrrrr), and had longish hair. After he hit puberty and got tall and angular (and grew facial hair!) that never happened again.
I'm petite and curvy, so I guess that's why I've never been mistaken for a guy, even though I've had shortish hair most of my adult life (longer now), and I tend to dress fairly feminine, though not to the extreme. Wearing makeup helps. 
Emily
Emily
2011 Jamis Dakar XC "Toto" - Selle Italia Ldy Gel Flow
2007 Trek Pilot 5.0 WSD "Gloria" - Selle Italia Diva Gel Flow
2004 Bike Friday Petite Pocket Crusoe - Selle Italia Diva Gel Flow