I am also having no problems. I personally have four systems running Leopard and I have absolutely no complaints. (One 'Aluminum' C2D iMac, one 'White Plastic' C2D iMac, an original MacBook Pro with C1D, and a Mac Mini with G4). All of my systems have been happily and speedily going along. No crashes, no headaches.
I use a wide variety of applications on these systems ranging from off-the-shelf games to command line utilities installed through MacPorts. Therefore, and expectedly, there were a small handful of applications I had which did not work immediately after Leopard's release. However, they have all been updated in the meantime and are now working great. In my case, none of these apps were remarkably critical; all of my most important applications worked just fine throughout. As a side note, gaming on my Macs seems to have received a noticeable boost in performance since moving to 10.5, which is really great.
So, make that two. Or, well, five.