I used to abhor collections and avoid it at all costs (my own costs, of course). But, now I've discovered that clients value your work only if YOU value your work. I've also learned that you need to educate them on exactly what it takes to create and maintain an effective site. I explain how that site will put $$ in their pockets. It's an investment, like any other advertising/marketing. Somehow the mention of value (translate: money) for them puts everything in a new perspective!
My favorite quotes:
"You can't take my site down. We use that to sell our products."
"I spent #3,500 on brochures that I mailed out! I need that site up right now."
HAHAHA You have to wonder at peoples' logic.