We use it and love it. It has increased our booking price on average of 7% and we're booked 92% of the time. While I used to agonize over the price and if I would get a booking, now I let smart pricing do it for me. I do watch for the weekends I know Smart Pricing might not catch an event or special occassion in town (especially those dates further out than the 4 month max). Plus, they are willing to lower the weekend price earlier than I would - so December weekend prices are starting to go down already but I'm not ready to list lower just yet - so I override the prices when I think I can still get a premium even if Smart Pricing does not. I do this for holiday weekends too, when I don't "really" want a guest but I'm not blocking the date either - like Thanksgiving. I artifically inflate the price in case there is someone willing to pay, but if not, I'm not upset that I didn't book.
My minimum is set at $43. Smart Pricing's closest "low" has been and is for $51 on a Wednesday in December. However, I have seen the opposite - prices rising into the $100s for high-traffic weekends. To me, that's a recipe for disaster as anyone booking my guest room for over $100 is probably going to have an expectation that is not realistic. That being said, we are already booked for those high-traffic days almost a year in advance (at $100/night - our max). Maybe Smart Pricing would have been a Smarter option.
Of course, we also like Instant Book as well and find the kind of guest who uses this feature is 1 of 2 types - (1) lazy and doesn't read the listing at all and then cancels immediately when you start pointing out that there is only one bed or dogs cost extra or we aren't located inside the Blue Devils stadium [read - annoying whether they use IB or not!] or (2) fantastic, high-quality, experienced guests. Luckily for us, the VAST majority are in the latter category.
With both IB and SP on, we find Airbnb to be a pretty agreeable system.
YMMV
