That Sigma sounds like a nice lens. I just acquired the 24-105mm which will be my new main lens for my 60D once it gets back from Canon. I'm sending both my bodies in for service to get dead pixels fixed.
i got my Sigma 28-300mm last year it came out just after Canon brought out the 20D i use this lens all the time for macro /close up street nature and so on
i had previously been using point and shoots but now i am learning everything about manual focusing and raw post processing