> I've never seen an SLA which is clear cut enough to be worth pursuing if you want more than a free t-shirt.

I have, regularly. I am not sure what kind of business you are running but parties that rely on service providers for critical (primary business process driving) components routinely agree to SLAs with large penalties and the ability to open up an existing contract in case of non-performance. Obviously you would have to be willing to pay for such a service in the first place otherwise there is no point in setting up an SLA, this won't be cheap. But we're definitely not talking about 'free t-shirts' here, more about direct liability, per hour penalties and so on.