I have been running WoBS for almost two years now, in a once a month campaign. We started in 3.5 and I have been house ruling into 4e as the team here is just barely catching up to us. We are at the end of Module #7.
WoBS is, by far, the best adventure path I have ever seen. However, it is what I would consider an 'advanced' module set as the GM has alot of things to track, manage, and adjust based on the groups actions.
On the broad scale, the adventure path ends in a Hobbitish 'war of 5 armies' and who is on which side depends on how the heroes did in earlier modules. Many bad guys are re-occuring and you have double-agents and people who just switch sides.
The initial modules are a bit rail-roady as the groups goal is to run away from the Ragesian Army, but after that you get into more free-form setups for the modules. One of the issues that the 4e version has is that they are adaptations of the 3.5 versions, in which you could easily have 7 combats in one session. Also, I think some of the writers should read Stalker0's comments on encounter building and anti-grind, as well has his Skill challenge rules.
Regardless of those issues, I am completely enjoying running a complex adventure with a strong back history. The path is almost a complete campaign setting.
As noted there is a sub forum here in which the authors, guiding publisher, and a number of GMs post about the modules. with HR ideas, adaptation for setting in published campaign worlds, etc.
Drop by and read some, and pick up the players guide and campaign guides.
And finally, being free for subscribers? thats a pretty good price that I wish they had when they started!
Ah.. Ninja'd by RW I see!
I am looking forward to the new campaign they have planned, but still would go with WoBS... in either 3.5 or 4e.