I'm not a believer in using astrology to predict the future, but I do believe in the time of year you were born having an effect on your personality, or at least a tendency to influence. I think it's more likely to do with the seasons or other natural environmental factors than certain stars or planets, or maybe even the mother's pre-natal hormones; but it does seem to match up with character traits more often than chance would allow. Has anyone ever researched this?
It would be interesting to find out how astrology developed and whether there was any logic behind it or not. That might be rather hard to do, as the basic art/science (leave you to argue that one out) has been around for thousands of years - ever since the Greeks I think, maybe earlier.
There's other, personally observed evidence I could cite to corroborate the personality-traits part of this hypothesis. I know two Leo's quite well who show typical Leo-like personalities in many ways. Both come from completely different backgrounds, they know each other well but only in the last 10yrs or so. I can display quite strong Taurus features sometimes, but be non-typical at other times. I am right at one end of the date-range for Taurus though. Obviously if everyone acted exactly how their star-sign said they should everything would be way too boring and predictable, we'd all be using it to our advantage and people would get used/taken-advantage-of because of it. My brother is an Aries and I think that has some matches too... So is it all just fluke/my human brain being particularly good at seeing patterns that aren't there (as we're all wont to do), or is there more... (cue Twilight Zone theme music to fade)
Extensive use made of Reference.com's Thesaurus earlier! Great tool when you know what you want but can't quite locate the exact word from memory.