The nice thing about "Library" is that it is a complete list (except for your inbox) so if you ever want to look at everything all at one you can. A competing product commonly referred to in this forum does not do that.
The way I differentiate most items is by context. I have both a work and a home context. There are a number of things I do regarding my home projects, when I am at work. So while I may be at work, I may be doing a quick item (print something, a phone call during working hours I can't do at night, etc.)
As for invoicing...
I have a project called "Operations" with a context of @Work. In it I have an action print & mail monthly invoices that repeats every month on the 23rd. This takes care of renewal invoices for clients that renew with me annually. I have another one to print and mail statements on the 1st of the month. I also have another one for weekly invoices on Fridays. This is for production work we have done that was completed that week but is not a renewal. Hope this helps.
Art
Art Wheat
SiteSteward, Inc.
http://www.SiteSteward.com