I'm 21, and I say we should wait for it...
As much as I'm starting to adore Shules (the last scene really did me in), I think it's better to test the waters a bit. Psych will only be in its fourth season (here's hoping it goes 900 more), and if Shawn and Juliet get together now, the writers throw away a strong storyline for the upcoming season. That storyline being Shawn with Abigail (that is if they bring her back, which I assume they will), and Juliet on the end where Shawn has been the whole time ... wanting Shawn.
Shawn has been wanting to be with Juliet, but she didn't want him. Shawn may still want her, but he can't let "the girl who got away" go again... can he? Well, sure, of course, he will... just not now, in my opinion.
If we wait for it, I'm sure the series will end with a psych-tastic wedding with Shawn and Juliet at the altar and Gus as the best man. Lassiter will be there too. I just don't know where yet... And of course, it will be funny in that awesome way that is not cheesy or lame (because that wouldn't be Psych!).