Oh, I have one. (Well, it was a couple days ago...but it'll count.)
Microsoft Excel has a row limit. Up in the range of 65000, I think. I was combining spreadsheets and it ran out of room! Easy to rectify, I just sorted and deleted extraneous accounts before I added more, but in my weird brain I thought Excel would go on infinitely.
I felt like I had found the end of the universe!
