From a designer's perspective, it IS important to be able to turn this off. Even if that's not necessarily the way the end user is going to see it, it's important for the
designer to be able to distinguish between different fonts, like offbeat said.
This drove me insane when I moved from OS 9 to OS X, too. Absolutely insane. I never really found a solution, except to "get used to it" (which I have).
One thing you should know is that you will never be able to disable smoothing for Lucida Grande, which is the system font. I think that might be the default font for Safari.
Like octavedoctor said,
Silk might help. I've never used it myself, though, so I'm not sure.
There's no built-in way to disable font smoothing for just one application, but you can approximate it if you're willing to go to some trouble. Here's how:
1. If Safari is loaded, quit it.
2. Disable font smoothing. If the settings available in System Preferences aren't flexible enough for you, download
TinkerTool.
3. Load Safari.
4. Turn font smoothing back to its original settings.
The key here is that when you change your font smoothing settings, it doesn't affect any applications that are currently loaded. So by changing it, launching Safari, and then immediately changing it
back, you guarantee that other apps will be unaffected. Just get into the habit of not quitting Safari, because you'll need to go through this rigamarole every time you load it.
If you want any new smoothing settings to take effect in all apps, you should log out and then back in.
Edit: Aliased text actually looks okay in Tiger. Last time I tried it (probably Jaguar) it was really, really nasty, with the letter spacing all messed up, but now it looks just like it should. Not bad.