Only read the following if this thread is making you twitch, tempting you to go spend that ~$1830 at the Canon store....the following is not meant for humorless fanboys
1) Canon Refurbished price though at first blush seems low at $1700, in the US, they do add tax (unlike many online stores), and that would be about ~$130 more on top of that price....so you hit that ~$1830 mark easy while you can have a new lens during rebate season for a few bucks more and get a a real box as opposed to the refurbished one and importantly a full year warranty as opposed to 90 days. Clearly, this is not a big deal, but if you need reasons to stall.
2) Let me think of other terrible things to dampen your ardor...lets see... The weight is significant as the sane already pointed out, it is also that obvious "look-at-me" lens for regular folk at venues, also keep in mind you get warts when you touch it and it leaks green gooey stuff when you are sleeping in your ears... and did I mention this lens stinks when you take it out of the bag? It smells like a mix between nerd and fanboy
3) Let's see...and the bokeh they say isn't all that pleasing...to see this you have to pick shots from the greyest winter day with a grey statue and grey bare twigs taken by someone totally unbiased and sweet shivering in the cemetery...can you live with something like the bokeh in that picture that I ...er...completely randomly chose?! Seriously! You don't need this... it is not good at all... awful... and if none of this makes a dent...think of the poor starving children of the world!
Note to fanboys: I am just trying to bring down the purchase fever others may have after the gormless fawing and lovefest that goes on here over this zoom. Relax.... I think it is a good piece of glass.