Out of all the applications I use excel has got to be the one that has saved me the most time.
I cut my teeth in C++ then taught myself VBA and my how powerful is it? I can manipulate data left right and centre, I can reference dll's and get it to control other applications. I can jump into any other vba program and work from there if I want.
On the downside I've seen some bloody awful coding over the years that takes you days just to figure out what the hell someone was trying to do. Macro's and variables without any meaningful names, references to macros that reference other macros for no point and hidden global variables that make where's wally(waldo) look shit at hide and seek.
If you ever use Excel VBA then one piece of advice I would offer is "Can you do it in a formula?" because 8 times out of 10 you are wasting your time writing a macro.
I have to say Excel is one thing Microsoft got right.