Wow I was expecting to read scores in the millions. I feel like Superman with my high score of 303,010.
I only broke 300k (and just barely) once, but I've topped 200k several times, and 150k pretty much every game. I use no hacks or cheats, just good old-fashioned shootin' and dodgin'. I get the double ships on Stage 1 and hang onto them as long as I can.
The secret to a high score in Galaga is to get a perfect score on every Challenging Stage. If you calculate the difference between getting 39 and 40 bad guys, it's staggering. You lose the points for that one guy, plus you lose the little bonus for getting all the guys in that particular wave, and of course you lose out on the perfect bonus for getting all 40.
My MAME says I've played Galaga 190 times since the last install which was about 2 years ago. 190 doesn't seem like a lot for some reason. That would be only $47.50 in quarters back in the day. But at 10 minutes per game (and a 200k+ game takes longer than 10 minutes I think), that's over 31 hours. Wow.
EDIT: Just saw Buddabing's post above. High score 1.2 mil, typical 400k. That's pretty impressive. His tips are good advice. However, when I lose double ships I get them back as soon as possible. I don't shoot the capture aliens, and when there are only 1-2 guys left, I allow capture and get the double ships back. Maintaining them is tough, yes, but with them you can better thin out the attack waves at the beginning of each stage, and without them it is pretty much hopelessly impossible to get perfect Challenging Stages which are where you can get big points.
Eric.