ok, ok. I could certainly live without these. they're way way below "air" and "water". but still, they make my job easier, and i'm grateful for them.
All you have to do is enable the developer tools (Preferences > Advanced) and Safari can be your new pretend iPhone. Just select a mobile device from the menu under Develop > User Agent.
This is awesome because I get to work in Safari, which I'm familiar with. Most useful of all, I get the Safari Dev tools, all there. "Inspect Element", "Web Console". This is huge.
In the end it is not a mobile device. The resolution, size and behavior are never going to be quite right so...
iPhone Simulator to the rescue
If I'm lucky, I have to turn to this only an the very end of a work cycle. A quick check, does everything look right, fit right, scroll ok? Done.
Sometimes I get into some trouble with autofill/autocomplete or similar and have to spend a good long time in the simulator. But I, myself, have an iPhone, and often I'll simply prefer doing that round of QA on the device itself.
Dammit Opera, where did my background go? The bottom of the toolbox or "break glass in case of emergency"
On my mac I also have an Opera emulator and an Android emulator. I would describe them both as "slow", or "frustrating", or maybe "terrible". I much prefer, in the case of Android, using an actual device. And in the case of Opera... um... hoping it works fine. But in the end, I do have to fire up these tools more often than I'd like.
And then there is my trusty Blackberry emulator. His name is Jason, he works downstairs.