Managed Services Provider Experience Out There?

I am in the process of evaluating managed services partners to provide 24x7 monitoring of internal systems (web servers/sites, intrusion detection, etc.) and I was wondering if anyone in the AO community has had any experience with choosing a managed services provider. The two companies with a distinct advantage are Symantec (with the acquisition of Riptech) and Counterpane.

Does anyone have any experience with these companies or other advice you would be willing to offer?

...aberration...