Appart from focus, the problem could also be resolution of the picture (but i doubt this is the case here, since you most likely upload the originals you took off the camery directly without processing, right?). For ideal results, make sure the pictures uploaded have a minimum resolution of around 800 pixels horizontally. The more, the better :)
I have the same problem with my digital camera, if the autofocus doesn't work 100% reliable, the picture just ends up blury... not much one can do, with the cats always moving around its hard to use manual focus etc. Unfortunately CSI-Style ENHANCE PICTURE ZOOM where you can zoom in without the picture getting blured had to be put off for picato 3.0 ;)
My guess is the original is not sharp... you can send it to me by email if you want me to look at it. But i just checked your other pictures, and there are definitively some very sharp ones (recent ones).
Old pictures had to be scaled up and will loose a bit of quality when zoomed in (the big view). But new pictures uploaded since of a few months ago should be as sharp as ever, provided the original is sharp..