My rule for any type of relationship is that if both people communicate what they want from it, and there is truthfulness from the start, then you know where you stand. If someone told me they only wanted to see me casually I could weigh up the options and decide if it was right for me.
If they didnt tell me til I'd already fallen for them after a number of dates, I cant say I'd be pleased. I'd feel led on.
There are some people I'll admit I'd settle for something casual with. Im single, it gets lonely, and sometimes all you want is a little physical affection. There are people I'd love to date but they wouldnt date me, so if being casual was the only way to get to kiss them etc, I would.
But...I can see myself getting really hurt, so maybe its not worth the hassle. :s
to be honest, casual relationships confuse the hell out of me. I'd probably fall for them by accident and get horribly hurt, unless I hardly fancied them at all, and then It wouldnt be much fun getting up to things with them as there wouldht be much chemistry.
Really, honesty is the best policy. If someone told me they only wanted to see me casually, I'd have that option to walk away.