I advocate every 6-12 months, even (or especially if) you're happy where you are. There's virtually no downside to doing this except for an unpleasant vacation day. Worst case is you still have your job you like. Best case is you get an offer that gets you a raise (either where you are or with a better company).
(Doing this I've gotten about a 10% raise every year for the past ~8 years - sometimes changing jobs but usually just presenting an offer to current employer - and I'm not a rockstar interviewer or anything.)
Enjoy your good fortune and be grateful. A lot of people hate their jobs. Even programmers.
Just make sure you're always able to get a new job if necessary. Basic stuff like keep learning something useful, don't tie yourself too much financially, etc.
The work is interesting, though never novel.
Everybody I know tells me programmers should change jobs every 2 years, but I feel like maybe I struck gold the first time?