I've seen worse, but not on my home computer.
When I worked at Tektronix I serviced oscilloscopes and spectrum analyzers and large multimeter's (among other things). Some of them had been built in the 70's, used constantly, and never opened up. We saw god awful things inside some of those units. Were I allowed to take pictures I would have.
Luckily We had a whole room set aside just for cleaning stuff. We had a couple of smoke hoods with air nozzles, and a deep sink with scrub brushes (for the cases). They were used quite frequently.
As for my computer: Fan filters do wonders. Even if I have to clean them every few months and they get destroyed after a year, they are worth it.