I have noticed recently, when I try to open the CK, that it will not open because Steam is downloading 'something' again.... About every 3rd time I open the CK it does this.

I look at the steam screen, and it says its downloading 'The Elder Scrolls V: Sky... - 15% 1.8MB/s

Usually when its a patch, at the bottom of that screen it says what its downloading and you can click the link, but this one says nothing.

Anyone know why on earth steam keeps doing this?

I noticed that too. My only guess is that for some reason it's updating every time they create links for tutorials to the CK. But yeah I noticed it too.

So I'm not imagining things then when I swear I see the icon briefly change to the "I'm downloading" version?

Cloud sync perhaps?

Considering I test my mod a lot, every third time I open the CK can be an hour apart. And its downloading megabytes of data. I really don't like Steams mysterious downloading of stuff to my computer.

No idea, however my internet is quite slow (download cap of 90kb/s) and it's taking me forever to get anything done because of this. I'm quite sure it's uploading, because it's only going in the 30s of kb/s. Very infuriating, to say the least.

Edit: I'm disabling the "Always keep this game up to date" and Cloud Sync options. I'll let you guys know if it stops this behavior when it finishes.

My upload cap is supposed to be 1.0MB/s, and its been higher, so I suspected it was downloading. Although, I woud not rule out it uploading data as well.

It's steam cloud, a system for syncing games over internet so you can play at multiple computers, it's also a backup system.
Recommend turning it off for skyrim if you don't use it. right click on skyrim then updates and take away the steam cloud checkbox.

I notice a patch that was downloading a few days ago and I don't know what problems you guys have, but I haven't got any problem with CK so far.

If it's the cloud sync, you need that to remain on or the CK will rudely tell you it won't start. You can turn it off for the game itself though, and I'd highly recommend that if you're like me and have a mountain of saves you weren't expecting to suddenly be exported without warning.