The fifth season was a great season, and this episode is one of the reasons why. In retrospect its all set up for later (the whole Monica and Chandler going away so that in the end Joey finds out and Ross having to tell Rachel he can't see her) but its done so well that you don't even notice.
The end of this ep has one of my favorite moments when Joey realizes about Monica and Chandler. The look on Matt Le Blanc's face always makes me cry and brings joy to my heart. Maybe if we could broadcast this episode to the entire world, by the end, there would finally be world peace. When anyone gets angry, all they have to do is think of Joey, and then be happy.
See, I'm thinking of him now, and I got no complaints.