Realistically, besides processing speed, what is the difference between the i5 and i7? Can you really tell a difference? I may be developing apps with it (I haven't tried yet, nor have I ever owned a Mac), so I'd also like to hear from a developer if there is a major difference or preference between the two.
i7 processors differ
I assume - since you are comparing the i5 to the i7 - that you are thinking of the 13'' MBP models. The 15''-17'' MBP models offer only i7 processors.
The i7 processors of the 15''17'' MBP are quad core, while both the i7 and i5 in the 13'' MBP are dual core.
2 important things to notice
An offical Intel documentation including all features of all 4 processors can be found here. The two processors offered in the 13'' MBP are on the right. Differences are highlighted yellow.