I just installed a 250GB drive and 10.5.1 on my MacBook, that had been running 10.4.11 on a 100GB drive very happily. The drive is fine but, so far, I'm an unhappy Leonard switcher. I can only relate two problems, and one annoyance, but -to me- they're biggies. 1) The annoyance: I put the old 100GB drive, with 10.4.11, in an external USB housing. I was pleased to discover the drive was still bootable, and I could run the MacBook from the housing. But when I installed Leopard (from the DVD), the Mac transfer program specifically said I had to connect the old drive with a Firewire cable. So I copied the old drive to a Firewire drive I had, and then ran the transfer program. THE TRANSFER PROGRAM WAS HAPPY WITH THE USB- CONNECTED DRIVE. Bringing over the Firewire drive had been unnecessary! The transfer from the USB drive "just worked". Why didn't Apple check and fix the instructions? 2) Problem 1: All browsers no longer do "domain guessing". I'm connected using Verizon DSL. Now, for example, when I type "jr" in the address bar (for jr.com, which is J&R) and hit "return", the browser loads the Verizon-Yahoo search page (with jr.com as the first entry). Old behavior: the browser would automagically add the "www." and the ".com". This is a major PITA; had I known, it would have been a show-stopper. It's repeatable; and happens on Safari 3.0.4 and Firefox 2.0.0.11. Camino works the same way. Strangely, it also happens on an old Netscape browser that had been "guessing" fine. While it sounds like Verizon is behind this, my wife's PowerBook, right next to me on the kitchen table, does domain-guessing like Macs always did. I found an about:config change that was supposed to fix this, but it didn't help. 3) I'll relate this in another post.