It would be good if it was possible to set a default "Billable" / "Non-Billable" status for a project - rather than everything defaulting to "Billable".
Why? Well some projects may have a mix of billable and non-billable items, but others (e.g. internal development work) will only ever be non-billable. It would save a bit of clean-up time if you could mark these to pre-set for non-billable. Presumably this could also apply to the other "modes" (estimate, PO), but really I think combining these four headings in a single field is a bit odd - as clearly you could estimate items that are billable and / or non-billable...
If this gets anywhere, it might also be nice to apply some thinking to the labelling / grouping of this field within Studiometry. In "Work and Expenses" view / dialog billable status is referred to via the obscure "Item Mode" label - but there must be circumstances where estimates and POs might want to include billable / non-billable information about activities - right now you can't. Separating the modes so they appear within two fields (one for Billable / Non Billable, and one for "Sold", "Estimated") would appear to make sense. I don't really understand how Purchase Order fits into this scheme, so don't know if it meaningfully goes with either.