DaveMage
Slumbering in Tsar
Perhaps Paizo may be creating their own "glut", by releasing three (or more) new titles every month. Though so far their books are of a high quality.
Maybe one day, an "adventure path burnout" and/or a "Golarion fatigue" may possibly set in.
As long as their products are products that *use* the rules and do not *create* new rules, I think they will be OK. By "rules," I mean player options. Too many player options can lead to an unwieldy game. It's my belief that in order for a DM to best handle his or her players, they need to be rules masters. (At least, they need to know their players' characters capabilities.) The more player rule options there are, the more likely that a player will find something that a DM can't anticipate and (potentially) ruin a game. Yes a DM can limit what books a player is allowed to use, but it's real bummer for a player to find something they think is cool in an "official" player's rule book that they are not allowed to use.
I really like the 1E model* for this, which is few player rules, and lots of DM support. Hopefully, Pathfinder will embrace this. 1-2 player-focused rule books per YEAR is OK, but beyond that, I think it's too much.
*3 player rule books (with classes) in 12 years: Player's Handbook, Unearthed Arcana, and Oriental Adventures.