We implemented OpenAir earlier this year, and managed to run out of space in our environment in just 4 months.  We we started with 10 GB of storage, and 98% of the used storage is for storage of receipt attachments.  We are a consulting company where we have about 120 users that are traveling 100% of the time and submitting an expense report every week.  Because we bill back expenses to the client, we require receipts for all expenses other than mileage.  Almost all of our users use the Mobile App for expenses and are taking pictures of their receipts