THANKS GUYS!!
I really appreciate it!
That was really helpful!
I have a varied range of Canon's flashes. If you need the 580 specifically, the Mk2 is the obvious choice. However, if you can do without the master options (like, if you own PW's new TT1/5's) and don't need that last power it provides over the 430ex2, the latter might be a better choice in terms of bang for the bucks. As mentioned in this thread, the 430ex2 is a really nice little flash - and at least in Denmark, you could almost get 2 of those for the price of one 580ex2.
Oh.. one thing I like about the ex2 series, is that they are able to power down to 1/128th.. whereas the old models only went down as far as 1/64. (This is true for the 430's... tbh I don't remember if it also holds true for the 580's)
Another note, regarding noise and PW's - apparently, if you own the european models, they are less suspectible to the RF noise from the speedlights than the US versions (We have to use a different frequency over here). Whether it holds true or, I cannot confirm yet - they wont be delivered for another month or so *sigh* (If you own PW's, you might want to look into the 430ex2 again, as that is supposedly a very good combo in regards to noise, compared to ex1's and 580's)