andreax81 - what is your invoicing procedure? As a freelance graphic designer myself, I have a hard time with invoicing. I usually have to go through my sent emails to make sure I invoiced for everything.
thadcoxdesign - Invoicing, or chasing unpaid invoices, becomes less of a problem if you use a water tight legal contract prior to starting work. If the client has read it and signed it they will pay on time.
I charge 25% of the total fee once the contract is signed, 25% once I start on the project and the final 50% is paid upon completion. They only receive the final files after I've been paid in full. This set up helps with cash flow.
I also use 'followup.cc' which is excellent. It works like boomerang on gmail and have a checklist for each project to help stay organised.