The internet can't really be treated as a single homogenous network. It's made up of many many smaller networks which connect to each other ("peer"). If you want to get traffic from say a residential connection in the US to a residential connection in Europe, you have to go through the US residential ISP (say Comcast), at least a few exchanges and then through the European ISP. The connections between these networks don't have infinite capacity and can definitely become congested. The network you're on determines the route you can take and hence whether/where you get congestion.
In my experience, it's usually not too big a problem with any major server provider and major ISP in the US until you get to about 100Mbit. At 100Mbit on Comcast, I start to have issues with Europe, depending on the particular AS over there.
Worth noting though that Linode has diverse set of peers so if there are issues they're more likely to be with the ISP on the other end than with Linode: http://bgp.he.net/AS63949
