The Good: 1)Stiffness 2)Highly Adjustable 3)Reliability 4)Race Support
The Bad: 1)Spring rattle 2)You will cry when you scratch your Kashima coated stanchion.
1)The 40 is the stiffest of the DH forks available. This can be an advantage or disadvantage depending on your weight, riding style, etc. Personally, I find this as an advantage. You can throw this fork where you want it in rocks. There is no noticeable flex. The fork does not wallow from side to side thru "gnar rox" like a Boxxer does. The stiffness can create a disadvantage in corners where you would want a little bit of flex to stop the front wheel from sliding out, but I don't notice it. I have heard some of my friends comment on this, however.
2)The 40 is extremely adjustable. I think a lot of people that rate this fork poorly have no idea how to set up a fork. Start at close to full open and go in from there until you find your happy place. Also, I highly recommend throwing on a pair of SKF seals. These made a huge difference in the suppleness of the fork on my 2011 40. Although it is not the most supple fork on the market, it should be smooth enough to please anyone.
3)I've found the 40 to be a very reliable fork. After 25+ days of Northstar, riding thru the winter, and the start of this bike park season, I have yet to blow a seal, damper, etc. I change the oil every 20 or so rides and that seems to keep the fork working well. It is also relatively easy to work on. There are no stupid pins/clips holding adjusters on the lowers that you need to pry off in order to change the fork oil(aka boxxer). It is no 888, but when compared to a Boxxer this fork is like a marathon runner instead of the slow fat kid trying to run a quarter mile(reliability wise).
4)Fox has amazing customer service at races. Want your fork rebuilt? Want 2012 dampers in your 2008 40? Go talk to them. You'll be amazed at what they will help you with.
1)Spring rattle. On every 40 I've ridden the spring rattles around. The easy fix is to throw a second elastic spring cover thingy on your fork spring.
2)I fell off a cliff at Whistler and put a dent in my left upper stanchion. I cried inside when I had to sell out 250 bucks for a new stanchion to preserve my Whistler trip. That's all I can come up with for negatives.
Overall, I give it 4.5 stars. Just because of the spring rattle issue.