I can't say enough good things about Nexcess.net. They host my Magento site and it's my understanding this type of shopping cart uses a lot of resources. That said, my site has been with nexcess over the last 2 years. It rarely has ever gone down. The rare times it has, they are ON it and even try to make improvements along the way.

The customer support is always extremely patient, friendly, and quick. They never give up. They always assume full responsibility for making you a happy customer. They are easy to reach and when you do they help relieve your stress.

You know, if you think about it, it's always a stressful problem as to why you'd be picking up the phone to call support in the first place, right? But they just always manage to turn it into a positive experience.

Really love them!