If you're working in UNIX environment then 60% is probably awesome. As a programmer, 60% is wicked when I use Vi. However, when I have to use a standard IDE, I find missing the arrow keys a bit of a pain. As well as being able to quickly press "End" and "Home". When debugging, missing the F5, F6, and F8 keys aren't really a problem. FN+number works just as well.
Go for it if you have the cash.
Now, I'm a Linux Admin, and and going to a 60% would be like cutting off an arm for me. Some of the utilities I use make extensive use of the function keys. Even in commandline, page up/down, home/end, and the error keys get a big workout. Smallest I'd be willing to go is TKL, and even then I'd be missing the numpad.
That said, I have thought about trying to make a layout where the number row migrated over and replaced the numpad. Drop the support for numpad arrow usage, ~ replaces NumLock, 0-9 in their traditional spot but shifts to use their extra character, same for + and -. Move down the function keys, get rid of the gaps, place backspace in at the end of the function row. Move Print Screen, Scroll lock and Pause over to the cluster with Insert and all them. This sort of of layout would be friendlier too for one handed typers.
