At the recommendation of the guitar tech at The Podium, I had a Baggs Element Active installed last March, and I really like the sound quality (people comment frequently on how nice it sounds).
The new strap peg (where the jack connects) was the only externally visible modification, and there's a volume control mounted just inside the sound hole, which is very convenient.
I'd recommend it.
Guitars: Takamine F-349, PRS Mira
Pedals: Line 6 M13 Stompbox Modeler, Boss TU-2 Tuner
Amp: VOX Valvetronix AD30VT, Ultrasound AG-50DS4