Will I get charge for transfering files between S3 accounts using boto's bucket.copy_key() function?
If you are using the copy_key method in boto then you are doing server-side copying.  There is a very small per-request charge for COPY operations just as there are for all S3 operations but if you are copying between two buckets in the same region, there is no network transfer charges.  This is true whether you run the copy operations on your local machine or on an EC2 instance.
I wrote a little script that copies files from bucket on one S3 account to the bucket in another S3 account.
In this script I use bucket.copy_key() function to copy key from one bucket in another bucket.
I tested it, it works fine, but the question is: do I get charged for copying files between S3 to S3 in same region? 
What I'm worry about that may be I missed something in boto source code, and I hope it's not store the file on my machine, than send it to another S3. 
Also (sorry, if its to much questions in one topic) if I upload and run this script from EC2 instance will I get charge for bandwidth?