MS Excel won't let you open two files that have the same filename. Even if they are different files (in different folders). Do you know how much this ticks me off? If I download a file from the network drive at work, edit the copy, and then decide to re-merge some of my changes into the original document, I just can't do it. I guess even with billions of dollars a year, MS couldn't afford to hire someone who's heard of absolute vs. relative pathnames?
Contrast with something like Vim, which will let you "open" the same file TWICE, i.e. the same buffer in two Vim windows. And when you edit one of them it will edit the other. And if you try to open an already-open file in another entirely separate instance of Vim itself, Vim will gasp ASK you what to do. Open anyways? Abort? Recover the other Vim instance's buffer?
My loathing of MS Office knows no bounds. If I had to rate the parts of Office according to suckitude, Access would certainly top the list, but Excel is a very close second.