I have both a PS3 and a Wii, and I so far have three games for the Wii, and I've rented only for the PS3 and downloaded demos - no buys, yet.
The high definition of the PS3 is stunning, and I'm going to take advantage of the Blu-Ray capability soon. I have the Blu-Ray releases of the first two Pirates of the Caribbean movies on pre-order with Amazon, due to ship in May around the time of the third movie's release, but I'll have other Blu-Ray titles before then.
But like you've said, the Wii is just stupid fun. I rented Rayman, and I like it, so it's a consideration for the purchase list. Second Opinion is a good one too. Wii Sports is addicting, same with Wii Play (okay, bump that previous count to 4 games for the Wii).
Right now, nothing for the PS3 has really caught my attention, except maybe Resistance, but the demo is good enough for now.
But Sony has a reputation for putting out big titles, and the PS3 will definitely follow that lead. Kingdom Hearts III (rumored right now, but heavily suggested) will be on the PS3, same with Final Fantasy XIII -- two huge franchises that have pulled a lot of sales. Tomb Raider is releasing a PS3 game soon, God of War 3 will be on the PS3 as well, and I'm sure there's more to come that'll be just awesome. Just look at all the huge titles that came out for the PS2, including Ratchet and Clank (those games were awesome). Speaking of which, I hope they make a R&C for the PS3.
So while the pickings aren't good right now for the PS3, just wait. I hope the Wii pickings won't go the same way as the GameCube with a few good ones and the rest as just "okay".