Congrats Paizo!
(long-winded post squished up below)
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I have had a feeling for about a year now that Paizo was approaching D&D's book sales, but I don't usually offer conversation on my "feelings" as I have been known to be wrong once or twice in the past and being wrong sucks.
It was kind of weird in my area. When 4e released, there were only 4e games at my FLGS (well that and Warhammer, and a board game here and there in the game room). When the Pathfinder play test started there still were no groups running it at the shop. I tried the system with a different group I play with that meets about once a month as they were deeply unhappy with 4e to the point were we were kind of throwing darts as what to play, and they LOVED it. It was like a 3.5 that had bandages over most the bloody game breaking parts of the rules. Yeah, even with bandages some of those hurt rules still gimped up the game here and there, but the game no longer bled to death in those situations.
But more importantly it was familiar enough that the players could navigate and they immediately felt at home, and it was new enough that they felt like there were new concepts to explore. And the game masters in that group already had experience with challenging the players and working with custom material for the 3.5 rule set, so it did not take them long to get used to the changes, and if they forgot a change and used the 3.5 version of a rule it usually did not have an effect on game play (unless it was one of those wounded rules previously mentioned).
That group adopted PF int he beta stage. My weekly group that plays at the FLGS did not warm up as fast, but when they saw the actual release and the quality of the material they changed over within two months. There was finally a PF game at the store. Over time some of the 4e players and game store randoms played with our FLGS group (we let folks drop in to our game and bring extra characters and character sheets just for that event because its fun to play with new folks. Plus the owner lets us play in his very nice game space for free, I figure the least I could do is play games with his customers so that they may be inspired to buy something).
Late last year one of the other 4e groups turned PF, and the other two weekly groups turned this year. I can honestly say that I did not see any evangelism or harsh words towards 4e. Most of the PF groups in my area own 4e books and gave the system a really strong go. In fact, most of them were WOTC only D&D groups through the release of 4e. To most of the groups I have talked to that switched the general concensus I got from the was that Paizo just has a more robust, better produced TTRPG than WOTC at this point in time. But the mean nasty fans that were previously mentioned seem to me to mostly exist on the internet were there is little to no real consequence for being rude or condescending. And I would also like to point out that anything that is popular enough to have "fans" usually has its share of d-bag fans as well. I don't think Paizo owns the patent on that innovation. But that being said I still don't see the mean fans previously mentioned. The folks that play 4e and the folks that play PF in my area are all gamers and they all hang out with one another, and the environment is pretty friendly.
After playing both 4e and PF extensively it is my opinion and wish that WOTC release more of the board games they have been doing recently. If 4e had released in board game form like the Ravenloft game, and books had been made to "advance" the concepts presented in those games, I would still be playing it in addition to PF and would probably have many more WOTC D&D products than I currently do. I have bought, and will continue to buy the board games using the system presented in the Ravenloft game. It is my opinion that those games represent the spirit of 4e's design philosophy. And its really cool to unpack it make a few simple choices and get straight into the game. It does not scratch my long term fantasy campaign itch, but it takes real good care of the lets go kill some monsters and take their stuff itch. And no one has to prepare anything. Plus as an added bonus, those few folks in my area who are die-hard 4e or PF can play the game together.

And the DM can take a day off. Heres to hoping WOTC keeps down the board game path. They are doing it right.
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TLDR: Most of the groups in my area who play PF started with 4e and I have not seen the negativity portrayed in previous posts. And I feel the board game rules system presented in WOTC board games like the Ravenloft game to be the best implementation of the 4e rules I have seen, and I wish they would make more of them.
And Paizo kicks ass.
That is all.
love,
malkav