Fibos - How effective are they??

Hi All,
A concept which is both fascinating and confusing is the fibonacci series and its application to trading. The fibo series goes like 1,1,2,3,5,8,13 etc where it starts off with 1 and the subsequent numbers in the series are obtained by adding the 2 previous numbers. I am just another trader like you all and i have no idea how these numbers came to be associated with trading. Why should these numbers and this series matter to trading shares and currencies? if this series matters, then why not the series of prime nos or series of odd numbers or series of even numbers or series of any other numbers for that matter?

I have no idea....but what we do see is that the fibo numbers of 1, .382,0.5 and .618 do matter to trading and are refferred to a lot by many traders and professionals. I have been trying to read and understand these series and also trying to use this in my trading. I have read a lot about this fibo series but still i am not clear nor sure about it.

Its not that something is wrong with the fibo but it might be just that i am very bad at it. If someone is good at this, pls enlighten me. The point that i find most confusing is this:-
The fibo points are usually calculated between 2 points but how do i determine those 2 points. Like for example, let me take GBPJPY a couple of days ago. I had pointed out that 239.7 was a strong support cos it was the 50% (fibo) retracement of the low of May 11 and high of June 5. But we found that the price broke thru that resistance and then bounced from 238.9 which was the 61.8% rectracement of the same move. So far so good. But how do i catch that the low of May 11 and the high of June 5 are the points using which i need to calculate the fibo?

In other words, i can take any 2 prices and calculate the fibos for it and claim them to be supports and retracments. I can take the high and low of yesterday, calculate the fibo and the fibo points (50%, 38.2%, 61.8 % etc) would be resistances and supports. Likewise, i can take day before yesterdays low and high and calculate the same way. Likewise, i can take day before yesterdays high (if it was higher than yesterdays high) and yesterdays low (if it was lower than day before yesterday's low) as the 2 points and do the same. Likewise, i can take last months high and this months low and calculate the same. Last years high and this years low and do the same. I could just go on and on. If i keep calculating like this, i would be supposedly having a support and resistance every 5 pips. Is that the way it should be done? How do i know which 2 points i need to take so that their fibos give me the strongest resistance and supports. If i do like above, i could show any price as the fibo retracement of any 2 pairs of highs and lows. So how do i determine which prices i need to take to calculate good fib retracements?

From the above, you guys can see that either i am talking great sense or i am so stupid that i have no idea of fibos. What do you guys think?