I've just started taking my girlfriend out on the bike. The problem we're having is that she's really tiny, 5'1, and for her to get her short arms around me she ends up with her neck bent back and helmet pasted into my back. Pretty uncomfortable for her.
I ride a 95 zx-6, and it has really good handles on either side of the seat but when she holds those she says she doesn't feel that safe because she's too upright and far away from me.
This isn't intense riding we're doing, we're just tooling around town with the occasional cruise up barnet.
The best thing we've come up with so far, is I actually put some large wooden blocks in the pockets of my riding jacket, which essentially gives her 'handles' on the sides of my stomach to grasp. But I'm not really sure how safe this is either.