How much rain does it take to ruin your ride?

I agree with everybody else that wind is worse than rain. People who don't cycle usually assume that rain is the worst thing, but I find that it always looks worse than it really is when you're not in it and I can't remember when I've last been annoyed by rain. It's just something you get on with.

Crosswinds can really destabilise you and headwind is obviously unpleasant. An additional problem are the turbulences created by large buildings in windy conditions. If you cycle past one unawares, it can really catch you out.

it does not properly rain for long here it drissels, and i don't mind that at all, but if its so bad that i can hadly see through it that will make me wait 15mins until it passes.

I've found the same thing--and in most cases of a downpour it's more like five minutes to wait. In London, it's generally not all that difficult to find shelter, either.