Happy ex customer of Freshbooks (ex because I am no longer consulting). I will say if you are disciplined and want to save every penny, you can get by with Excel and word for invoicing, but once you get your first client or two, Freshbooks is real nice to have. Easier, invoices look better, you get reporting.
And the Weinberg book is top notch. Anyone who wants to solve problems in business should read it.
I also use a tool called FreshBooks that has been killer as far as invoicing and tracking time.