Well, it looks like I spoke too soon about Snow Leopard's advantages for Chinese-language users. One of the things that converted me from Firefox to Safari was the ability to use the Services menu to convert simplified Chinese to traditional Chinese and vice versa. Unfortunately, Snow Leopard broke this with its new, cleaned-up Services menu. The new menu is a very good idea--only relevant services show up now--but it doesn't seem to recognize when you've selected Chinese text, so the conversion options are not available! This is probably a Safari bug, as the options are available most of the time in TextEdit, etc.
The work-around for now is to paste Simplified Chinese text into TextEdit, convert it, and paste it back to wherever I need to use it.
If you encounter this problem, please make sure to file a bug report with Apple.
The new Snow Leopard has a nice new input system for inputting Chinese: You can write characters directly onto the track pad with your finger. To toggle to handwriting input, press Control-Shift-Space... apparently. Unfortunately, I missed the part where Apple told us this would only work on multi-touch track pads--ie., those on newer MacBook Pros, MacBook Airs, etc. My old first-generation MacBook doesn't support Chinese handwriting input.
The good news is, though, that the Pinyin input system seems to have been updated. I haven't messed around with it extensively yet, but it seems to be better at predicting which characters you want, and, when inputting Traditional Chinese, you no longer have to put in numbers for tones. (I think this is how it always worked for Simplified Chinese.) Just type in "nihao," press Space, and it knows you want 你好. I actually prefer to type tone numbers so as to limit the number of candidates that come up, but I could see how in some situations this could save you some time.