Okay, I consider my English to be pretty decent, but lately I've been very confused about something very basic that you get taught at the most basic level when studying English.

Possessive forms: 's or -s. I thought it was supposed to be -s unless the word ended with a vowel. So Sid Meiers instead of Sid Meier's and Angela's instead of Angelas. But just adding an -s to a word just feels wrong, is this because I've spent to much time on the net, where nobody bothers with such things as correct grammar ? Or should it always be 's ?