I don't see a problem with holding hands, as everybody seems to do it even Qatari couples.

I don't either think that they will arrest someone for a peck on the cheek because this is done all the time too.

What I believe to be forbidden is when a couple walk with arms around the other's waist or shoulsders, and kissing on lips and hugging.

And those who were caught because they were in a taxi together only dosen't seem realistic. What were they doing in the taxi? Were they drunk? What was the girl wearing? I think there's more to it than just being in a taxi together.. I go out all the time with my driver and never been arrested for it :)