I like them – been riding them for ages so it seems like the natural fork for my bikes, I've actually never ridden a standard short travel fork. They are absolutely as stiff as a board – this is probably the main selling point (although strictly speaking I don't have anything to compare it with myself). It's the type of fork that is really suited to a short-ish travel XC bike IMO, something like 100mm. Think you can get longer travel leftys – not tried them though.
They need to be looked after, and are a lot more difficult to work on than your typical fork. I used to think that this was a real hassle, but the flip side is that they are very durable. They last years if you keep them maintained. Tony at thumbprint can get a first generation lefty from ten years back working flawlessly.
They're also pretty cool from an innovation pov. Seems like the bike industry is big on boolshiet marketing non-ideas, and short on real engineering ideas to try things differently. CDale have come up with a decent, new idea that works, and actually stuck with it. I like that.