Tell me about it. Bought myself a lovely MacBook in May, running 10.4.8 ... all lovely.
Updated to 10.4.9 and my wifi internet connection stopped working - transfer speeds dropped to about 2k per second when it worked at all. Tried the Airport patch that fixed this issue for some people. Nothing. Rolled back to 10.4.8 and all was well.
Then Apple announced that they were making changes to .Mac and you'd need to run 10.4.9 or better in order to sync properly. This wasn't an option, so I waited, with a crippled .Mac account, for 10.4.10 and dutifully updated.
Guess what?
Wifi internet FUBARed again, so I had to roll back to 10.4.8 ... which means that I am currently paying for a .Mac account that I cannot use with my portable machine, due to a known issue with Apple's own operating system.
Thanks, guys. After fifteen years of dedicated Mac use, thousands of pounds of my money, it's embarrassing to be stuck in this situation having recommended my Mac experience to so many people.
Bah.
Jim