I'm often running into the problem, that I don't know how much space I have to place a view.
There's 20 units reserved for the status bar. How about tab bar, navigation bar, etc.? Sure I can look that up, but is there any good graphic on the net that shows all those heigths?
Let us know!
Another is in the iphone Developer's Cookbook by Erica Sadun. I have it and it covers all of the heights and frames for portrait and landscape mode.
I can't post the image obviously, but you can acquire the book for yourself: http://www.amazon.com/iPhone-Developers-Cookbook-Building-Applications/dp/0321555457
Not the strongest of the iPhone developer texts, but does have some useful things, especially when it comes to programatically laying out views. (It was mostly written before IB worked for the iPhone)
I have found that after a couple of months of iPhone work, you will have all the standard sizes memorized as well as the ones specific to your Apps.
I find myself using the built in mac screen shot utility quite often to measure pixel dimensions of elements on the simulator. (Command-Shift-4) I draw the box to the size I need. jot down the dimensions and then his Escape so the snapshot doesn't happen.
Its also useful to note that in IB if you select your view, the first panel of the attributes inspector has the "Simulated Metrics" section - where you can simulate adding the Status bar, Top Bar and Bottom bar. This shifts your view so that you can see how it will look with these things added to it.