From what I've read, some people have had rubberbanding since the game came out.
I started playing soon after Factions came out, and never had any problems with it. Even when I was running all over Tyria, which is when I usually see it now myself.
But as soon as Nightfall came out, I was doing a run in Tyria and experienced it for the first time. Ran through a mob, was way past it, but still getting damage while out of agro range of anything. Used a skill that you have to stop to cast and BOOM teleported back to the group I had run through.
So for me, I've had varying problems with it ever since NF came out, where I had no problems with it before. This was on 2 different computers, in 2 different locations.
This is also when I started to see more and more threads about rubberbanding start to appear on the forums.
So while I'm sure that some of the people complaining are having problems with their PCs or with their net connection to ANet's servers, I'm also certain that the number of reports and with the complaints of the problem starting at the same time, that this is some kind of bug with the pathing logic of the game. You might notice this if you are running at an enemy (not targeting and hitting space bar, but just running) and then try to cast a targeted spell. You'll see your character jump a little bit before you cast.
For me it's not game breaking, just means I have to be more careful, and it makes certain choke points on various runs more...exciting.
The endless aggro bug was worse though. And ANet was finally able to identify and correct that problem. I hope that they will be able to improve this problem as well some day.