If you're talking NASDAQ, I think it's about as real as it gets cause everything is electronic. And you have the ECN's in there competing and always trying to shave milliseconds. With a good connection, you're probably about 1/10th to 2/10th of a second away from when the trade occurred (time to get excute + time for the ECN to process it + time for the ECN to send it to your data provider + time for your provider to send it to you + time for your PC to display it to you).
If you're talking NYSE, then it's a different story. The specialist can be talking to the people in the crowd, perhaps "working" a big order. The broker doing the order knows he's going to get it and the price, but by the time the specialist gets everything going, it may be 20-40 seconds before he puts it on the tape. I know this because I've had trades where I get the report 20-40 seconds before I see it on the tape and this isn't due to a slow connection.
For anything traded in a "pit", you'll also be behind by a number of seconds. Though, not sure what the number is.