I'm on a complete tangent here, but how hard the PCs are to track is more a function of how lenient the GM is than how careful the players are. Well, obviously clueless PCs make the job easier for the GM but still.

My PCs are usually reasonably careful as players go, if I judge by the stories doing the round on the net. I remember an instance were PCs had rented a car under a false ID while operating abroad. After a firefight that left the car a wreck, one of the PC thought about removing the license plate and torching the car while the decker tampered with the rental agency site. Still they realized that serial number of pieces of the car would allow for identification of producer and that would lead the cops to the buyer and then the agency could inform the cops about the runner who rented the car even though that info no longer was in the computer system. From that info they would check with the airport and find out who came in with whom and when while using that ID.

But they hoped to delay that long enough to get out of the country before the fake ID burned in their hands. They immediately proceded to get out of dodge and I felt so proud of them I didn't bog them at the airport. It almost brought a tear to my eye. They really did the best they could under the circumstances and time limit they had.

But no matter how carefully they covered their tracked, they still left plenty during the firefight (which they didn't instigate). Witnesses, footage (it wasn't a barren), all transaction logged under these fake ID etc. Cross referencing with the airport cameras would ID them and their destination, for example. Or then again the opposition could simply track down the employer. It's often easy enough to figure out who benefitted from the run. Unless you are dealing with a Lofwyr type of plot, the one who benefits hired the runner. Sure, you have no proof but who says the cops are doing that particular bit of tracking? If the opposition are bigger fish then the employer, they can make him cough up how he contacted the runner if they need to. Heck, that's exactly what happens in the first adventure of Wake of the Comet. Not much you can do to prevent being tracked down in that kind of scenario.

But even if you manage to be a total ghost, PCs usually stay on the market for more jobs so there's not much they can do to remain completely untraceable no matter how paranoid.

How many runner are there in Seattle (for example)? How many within the talent range of the PCs? That's right, if an enemy needs to track the PCs and he has nothing to go on but the city they operate in, he just has to let it known through the grapevine that he's looking for runners fitting X criteria for a run. He justs co-opt a respectable fixer to do the asking and sooner or later the runner he seeks will meet a Johnson under his control and voilà.

Unless the runners retire and never again get in touch with their old contacts, I can set up a believable scenario in which they are tracked down for every run they make. How careful they are only benefit them through the amount of warning they'll get before any trap can snap shut. Being fair minded I will let them use that benefit for all it's worth and careful runner stand much better chance of surviving.

It comes down to how badly your last victim needs to track you down. Usually he doesn't and goes on with business as usual. But often enough you get a Cyberpunk twist and it happens. Then, if he has enough ressource, he'll eventually find you though it may take time.

That was just an aside. That comment about extra-paranoid game reminded me of a GM friend who felt he couldn't have a certain opponent track down the PCs because we had been so careful. My answer was essentially 'Are you kidding?' and I enumerated 4 distinct ways it could be done. And I was one of the runner in question and I can assure I had taken all the precaution that were reasonably feasible. (Yeah, we occasionnaly chatted about the game because I had more GM experience and he trusted me not to abuse it).