I've found that I often use colons in technical documentation and emails, yet I've probably never 'really' understood quite how they or semicolons should be used. I think my school days were after the golden age of English Grammar education (or maybe I just didn't pay attention).
After reading this, I'm now clear on the picture. I could rephrase that as follows (just to force a semicolon in):
I read this article; I'm now clear on the picture, and shall use semicolons to appear clever.