There is a really nice new feature from R2 onwards in the Project management and accounting module for project purchase orders.
There is a new checkbox in the project accounting parameters, called Create item requirements.
What it does is, when you create a project purchase order, it creates automatically for you a marked item requirement on the project purchase order (and not anymore the annoying virtual inventory transaction which makes upon receipt of the project purchase order, items are consumed immediately on the project).
Upon receipt of your project purchase order, the popup still comes where you can choose to consume the items immediately, but you don't need to do it. Making it possible to ship actually after receipt of your project purchase order, your goods on a latter moment in time and keep it in between in your warehouse (and probably break the marking and reservation so you can use the bought goods for another more urgent project).