I am sitting pretty waiting for the 5DII's to get in good circulation, then decide if one of them or a 50D is the macro shooters choice.
The 50D has the highest pixel density (and therefore detail) of anything out there in that range. Some say it isnt as good as the 40D at high ISO (though there will always be debates for and against that argument!). At the end of the day a shot at ISO 64000 or whatever is gonna look shite whichever way you look at it, so you can have (possibly) a slightly less shite image from other models at that level if you want. I'm intending to shoot in the 100-400 range mainly as will most others so that's not really an issue.
With the 5DII however I can have an almost umthinkable luxury of downsizing to print to A3
The reviews will be out soon then I can choose Then again there could be a 1D MKIV just around the corner, if that had 15MP+ oh boy.... though the fixed grip would be a bit of a pain!