A few things:
1) People lie a lot. I'm not saying that EV1 is lying, but it's possible that they're exaggerating or are offering misleading or outdated information. A lot of companies (and I don't think that EV1 is one of them) like to describe their provider's network and then talk about "their" network.
2) EV1 is a totally different type of company. They have a lot of "customers" who are resellers and have customers of their own. They have a lot of dedicated server customers. It's pretty likely that they are pushing a /lot/ more bandwidth than we are overall. We have lots of small customers, and some medium-sized and big-ish customers.
Also, with a lot of dedicated servers they don't manage directly, and with all the layers of resellers, I imagine it's harder for them to deal with some sorts of attacks (both inbound attacks and outbound attacks from compromised machines).
Ultimately, you're comparing apples and oranges here... the "number of customers" isn't really relevant.
3) As Dallas says, we're always running below capacity. If the need arises, we can add additional capacity on very short notice. If a single Gigabit link fails, the other would be able to handle all of the traffic plus some. The FastE line is normally running well below capacity. We will be either getting rid of this line entirely after the router upgrade I mentioned, or will be getting a third Gigabit line.
4) We monitor our uplinks to various providers on an ongoing basis, so that we can identify problems and keep an eye on traffic trends.
5) Remember that network bottlenecks aren't necessarily at either end point.
6) Having lots of different providers can be a good thing, but it's not always that important. And keeping prices down is usually easier to do when you're dealing with fewer providers with a higher commitment to each provider.
In any event, don't take our word for it, and feel free to do some testing of your own by downloading big files from people hosted with us... overall, though, I think we run a pretty solid network, and I think you will be happy with it.