yeah, i have been keywording with cs3 bridge and haven't had any problems. 

I would double check the actual files you uploaded to shutterstock to make sure they still have the keywords attached.

If you are processing images on shutterstock, while more are uploading - you can also run into problems with keywords not being attached when you click 'submit' and more images come onto the list (if that made sense)... but all you have to do is reload the page.

I had the same problem and found if I keyword before I post process I don't lose anything after I upload, although I use cs2 not cs3.

nataq - Bridge locks use of the file if you have the file selected (in Bridge).  So if you keyword a file in Bridge and then upload it (while still having the file highlighted in Bridge) none of the IPTC info will get 'released' from the file for upload.

Other than this little quirk I use Bridge all the time and find it excellent.

However I have gone back to Bridge CS2 instead of CS3.

In CS3 you have to remember to 'save' the IPTC info as well - by clicking the tick icon (although often it saves without doing this); CS2 doesn't require this which is why I've gone back to using it.

In short, Bridge is an excellent program, butI use CS2 instead of CS3 because it has fewer quirks.

As far as I am aware the problem only occurs when you have the file selected/highlighted at upload stage.  Naturally if you have multiple files selected/highlighted they will all be affected.

Best thing to do is try it out: select a file in Bridge then upload it to iStock and you'll see what I mean.  Try again without it selected and you'll see the difference.

Couple of tips if you haven't already worked them out:

I use the 'file info' box for IPTC.  Right click and select 'file info'.  You'll see arrows on the left which you can use to pull over info from previously edited images.

Also, if you haven't already done so, create a template for your artist and copyright info etc, then when you upload new images to your computer use the bridge upload tool and you can tell it to automatically add your artist info at upload stage; this process ensures that every image you upload to your computer automatically has your info added and you never have to worry about remembering to add it later.