We do not have TippingPoint devices in either DC and most likely we never will, at least unless we'll decide to triple our prices. It doesn't make much logical or financial sense to put application-layer intrusion detection/prevention device with price a tag of $100k+ in front of the $20 VPS...
Also, what kind of DOS attack are you referring to in this post? Small scale service-specific as computervitals is talking about? We do not monitor such things for very simple reason - if we'll do monitoring/filtering of traffic based on, say, number of connections some specific IP is establishing to the service running in customer's VPS we will a) have a lot of complaints ranging from "server being down" to "you're killing my business" and b) such things won't help with scenario described by computervitals. So, at the end we'll bring more harm and havoc with very low (if any) positive effect.
If you're referring to low/medium sized network attacks directed against one of our customers, then our position wasn't changed since last year: http://forums.knownhost.com/showpost.php?p=1363&postcount=7
If you're referring to DC-wide attacks that bring the whole DC's network down, then it doesn't matter at all what kind of equipment will be installed in front of your VPS. Even if a million-dollar device is put in front of the specific VPS it won't help at all if uplinks are completely saturated with traffic that, in some cases, isn't even reaching us.