Well in Scotland, Killie would be the obvious "not exactly setting the heather alight" example, though of course they've only had theirs a few months so far. (It does look to be a better quality surface than NDP though). I'm sure Alloa do get some better results on their pitch than they would on grass, but I'd suggest that's still at least as much down to other teams' unfamiliarity/fear of it, as to any attributable improvement in Alloa's silkiness of football since they've had it.
Overall, of the 12 SPFL clubs who currently have artificial pitches, their average league position is a decidedly mid-table 6th, which (admittedly without having looked into them in any more detail) doesn't suggest to me that they're having a measurably positive effect on those clubs' results in themselves.