I check the bike after every ride, and address maintenance issues immediately.
Every five years, whether it needs it or not, I take the seals off my Chris King headset, clean, and apply new grease. (I use the Gen 1 lifetime supply ring-lube grease, which they recommend.) Then I put it back together. But it has never looked like it needed maintenance so frequently.
Winter is the time when you guilt-trip your S.O. into permitting you to purchase a new bike.