Well this is frustrating. It seems some of the stuff I like has already switched over to Flash 11, but that won't run on a 10.5 OS. :/ Is it worth downloading OS 10.6x?
10.6 is worth it for me, it is the best Mac OS X version since 10.4 for me. 10.7 and 10.8 are not for me though, too much iOS-ification.
Also know, that 10.6 cannot be downloaded "officially".
PS: 10.6 does not deviate from 10.5 that much, at least visually, as the most changes were made under the hood (getting rid of PPC code, introducing new APIs, and so on).