would we not currently have (in 2011), time travellers, visiting us?
Not if the time travel only went in one direction (forwards) and was developed in the future - although I'm sure some might argue that there is no concept of direction when it comes to time. Also there is no guarentee that even if we were visited by time-travellers, that we would be aware of their presence.
I've experienced Deja-vu before a couple of times but unfortunately the first time I 'experienced' the events I wasn't aware that it was actually a premonition of a future event.