I used to work in credit control but am crap at chasing my own invoices.
This is part of why I like working through sites like People Per Hour - no hassle and when things are overdue they do the chasing for you. One client I invoice myself and is a little forgetful, but a polite email saying "hi, did you get the last batch of stuff as the invoice doesn't appear to have been paid" usually does the trick.
Also I put shorter terms on my invoices - 14 days rather than 30 or 4 weeks.