Dang, you guys have me feeling guilty. I'm off to the LFS to buy some saltwater.
Over the last several months, I have gone from religiously testing to religiously observing and depending on that. Maybe not the best habit, but I feel comfortable taking a good look at my tank and knowing what is going on. If I see some cyano/dinos I test my nitrate and PO4 and start watching the skimmer output, if my LPS aren't extending as normal I test my alk/CA.
If things generally don't look great, I check pH and salinity and change my carbon bags.
Other than that, about 10-15% every 2 weeks-month, clean the skimmer cup when it gets full, and drip kalk every night.
I scrape the glass whenever I want to take some pics.
T