I'd say, from bitter experience, you definitely need a second cleans if wearing sunscreen. Result of skipping out on this, in my case, was pizza-face zit city :mysmilie_51: My own fault for being lazy... I've taken more care to scrupulously remove all spf before bedtime since.
That's been my experience too. I have some health conditions that cause me to sleep excessively and frequently fall asleep long before bedtime. Half the time I don't make it to bed and am asleep on the couch all night. No one can wake me up no matter what they do; shouting, pulling my hair, throwing water over me... I don't even stir. If I fall asleep with sunscreen still on my skin, or indeed most make-up, my skin goes berserk with spots.
If anyone's interested, the one thing I've found this doesn't happen with is Bareminerals. If I sleep with their foundations on my skin's fine. Obviously I don't exactly deliberately leave it on, of course not, and I'm wearing make-up less these days to try and avoid that happening, but it's still happened enough for me to know this.