Okay, most iPhone developers have likely discovered the Apple Bug Reporter and have likely used it on more than one occasion. If you're one of the few who haven't, though, there's the link right back there. Bookmark it, and use it. Use it for bugs. Use it for enhancements. It is the one and only official mechanism for letting Apple know about both bugs and things we don't like. Posting to forums or mailing lists - even those run by Apple - does not get your complaint in front of anybody with the ability to fix or change it.
If you do use the bug reporter, though, make sure you're thorough and follow their format. Give them detailed replication instructions. And, be formal and polite. Remember: a real person will be reading what you write, and that person may very well be the programmer who wrote the code that you don't like or think has a bug.
Here's a little thing that confuses a lot of newcomers to the Apple development world - those darn Radar URLs, the ones that look like this : rdar://problem/12345. They never work, do they? The reason is that those URLs aren't meant for you, they're meant for the internal Apple engineers with special software installed to let them access the Radar bug tracking system. There's not even a way (that I know of) to map those URLs to RadarWeb, the web-based bug-reporting tool that we all have to use, and even if you could, RadarWeb is not going to let you get to reports you didn't create or are otherwise linked to
So, next time you see one of those rdar:// urls, just remember, it's not for you and don't bother trying to click it, okay?
Wolf Rentzsh has a little more information on Radar URLs, including the format and why they're used outside of Apple.