There seem to be two types:
Those black-
homepage, bare-it-all-online
teenage girls, the ones with too much
artistic ambition and not enough
self esteem. They write angsty and sometimes
pretentious poetry and are using the lowercase "i" intentionally, to project a certain
image.
Then there are those who are too lazy to capitalize anything, and, in addition to the drastic grammatical transgression that I describe here, also like to use the (lowercase!) letter "u" in place of the word "you".
You cannot spend more than a few days online (unless you only look at business webpages designed by people who are paid to have good grammar) without running into some variation on these two basic personality types. They are a necessary and necessarily annoying part of any online community.