I'm constantly uploading things from Skitch & find it really handy.
What I'd find really useful would be once you've clicked 'webpost to Flickr' the Skitch window flips around to show a 'Flickr info/organise window' where you could add tags, add to an existing set/collection, description, groups etc. (Kinda like the FlickrExport iPhoto plug-in but for Skitch).
Also an option to alter the tag Skitch automatically adds (I just want it to say skitch in lowercase :) ).
I can't upload to flickr today. It used to work, like yesterday. Also, the rest of the internet works perfectly fine! I haven't changed any settings in Skitch or in Flickr.