To buck the "simpler is better" trend just a little, I am a big fan of dripless shaft seals. Having had experience with all three basic types (lip seal, bellows-type, and spring-loaded), my preference, without question, is the Lasdrop Gen II spring type.
The potential for a very bad flooding event has already been mentioned for the PYI (and other) seals where a flexible rubber bellows is used to keep pressure on the two faces of the seal. Otherwise, actually, these are not bad seals. Just keep an eye on the condition of the bellows, clamps and keep the seal faces clean.
The lip-type seals also work very well and eliminate the chances of a major flooding event due to the simplicity of the design (a rubber lip riding on the shaft). As a bonus, there is no occasional adjustment that must be made. The big disadvantage to a lip-type seal is that, eventually, it WILL wear a groove into your shaft. Once that groove becomes pronounced enough, the seal will leak. The only fix is either replacement of the shaft ($$$$) or, if you are lucky, you will be able to move the seal a bit to get back to a non-grooved section of the shaft. There are several ways to do this, but the biggie is that you must have enough room on the exposed part of the shaft (between the flange and the shaft tube) to move the seal location.
The best option, in my humble opinion, is the Lasdrop Gen II seals. These seals do not use a rubber bellows to put pressure on the seal faces, but rather use an internal spring. Go to their website for a much better explanation. As far as maintenance, as with any face-type seal, occasional cleaning of the seal faces may be necessary - but it is a simple task requiring only pulling the two faces apart (or potentially loosening the fixing clamp) and wiping carefully with a clean, soft rag, then readjusting the spring/bellows tension. If I was building a new boat - or refitting an older one, these are the shaft seals I would go with.
But, to answer the original question: "Are Dripless Shaft Seals Really Maintenance-Free?" Well, that has two answers: "Dripless?" Yes. But "Maintenance-FREE"? Nope. EVERYTHING on a boat requires SOME kind of maintenance!
ERIC