My tip-in is on poets. Someone asked me to explain how a tip-in works. Instead of your journal being mailed to someone new to work in every month, an assigned artist makes the pages for your journal according to your theme and mails them directly to you. You get to watch your book grow! Each month you are assigned a different person and you make the pages according t their theme. The upside is that you get to see your pages right away and it saves A LOT on postage. The downside is that you can't see the other participants work in other people's journals.
I've only done RRs and they are wonderful except the postage is a killer. It's also really awesome to get your completed journal back at the end after it's been gone for a LONG time. This is my first tip-in so I can't tell you how I feel about it yet. All I know is that I'm very excited for it to begin!