Never ride without them except in colder weather. I bought my first pair 11 years ago, and I finally had to get a new pair last year. I can only vouch for Shimano sandals on Shimano pedals, though. They will work as well clipless as any other SPD-compatible shoe. For me, cycling is not about pretending to be a racer or about dropping people, it's about being out in the fresh air, moving under my own power. No closed shoes for me, but I have also used other cycling shoes (now either sold or gathering dust), and so I can confidentally say that the sandals work just as well. Now, that being said, I did prefer the older Shimano sandals over the new ones. The new ones have more rigid support, but they are less open to the air.

I have several different clipless pedals, but I really like my Shimano M323's the best (that's the one with the regular pedal on one side). I find that these have a bit wider support for the sole than regular SPD pedals. Sometimes, on more casual rides, I just use whatever other "civilian" sandals I happen to be wearing.