I know I always complain about block swapping and swear I'll never do it again, but the HGTV CYOC (choose your own color) String Block swap is different. I really like making and swapping string blocks. It doesn't matter much who you are swapping with. The newbie can't screw up a string block so bad that you can't use it somewhere. And as for the seasoned pro, it's a super easy way to clear out your string stash and get some blocks done quickly.
If you would like to join in on the fun ( or just want to follow along) you can get all the info you need here at the HGTV CYOC thread