I will suggest you to search for their legitimate reviews at places like HostJury, WebHostingTalk, RatePoint, etc. This will give you a better outlook on how their clients thinks about the company.
Oops. I didn’t articulate my thought very well. I would like to know peoples’ experiences with using Magento on Slicehost; not so much peoples’ opinions on the host. You’re right--that can be found all over the web. But I haven’t found anybody really talk about how well Magento performed on Slicehost.
port23user: ask them to provide you with a demo store, then you can check the performance yourself. I would hesitate to buy Magento hosting without testing their speed first. A host that is fast for some people might not appear fast to you, so do not only rely on other peoples reviews.