I voted that it is way too fast. By that, I mean that the defaulted XP system is far too fast. Adjusting it to the style and speed of advancement you desire in your campaign is not difficult, but should be discussed more in the DMG -- in my opinion.
I think advancement should drastically slow down with each additional level. I feel each additional plus and ability should feel like it was earned -- like you accomplished something. Right now, it comes a bot too quickly for my tastes...
For example, in my current game the XP chart is like this:
Party Power = (Total character level of all members of party) / 4
Difficulty = Challenge rating minus Party Power
Difficulty ... XP Awarded
========== ... ==========
-6 or lower ........... 0
-5 ................... 10
-4 ................... 25
-3 ................... 50
-2 .................. 100
-1 .................. 200
0 ................... 400
+1 .................. 600
+2 .................. 800
+3 ................ 1,000
+4 ................ 1,250
+5 ................ 1,500
+6 ................ 1,750
+7 or higher....... 2,000