@David I. - I've seen situations where "friends" pooling money together works out well and other situations where it becomes a huge disaster. Besides having a successful project, the common factor in whether the arrangement is successful or not are: transparent roles, leadership, legal/work responsibility, stake, costs/fees responsibility, and exit strategy.
Also, from that i would add, much like accredited investors, you don't want to take $5K or $10K from "friends" who could arguably not afford to lose that money.
To answer your question, the level of return they should expect should be outlined as part of the stake I mentioned. The payout can be a percentage tied to the equitable portion of their investment, or it can be a flat fee for usage, presuming a set profit margin is reached.
As far as success stories, I personally know of a group of about 7 friends who have all been in the real estate industry for years. They decided to pull their monies together to start a fund to purchase and rehab higher end homes and some commercial properties. Granted, their pool of funds is in the millions (some provided much more than others), but the transparency I mentioned above has allowed them to successfully purchase properties, conduct business, and above all remain friends.