What's Hot:
If the sort of art provided is to your liking, then having six million items to choose from gives you a very good value. It's certainly a far greater number of images than any of the offline solutions.
What's Not:
The downside of the price to value for Clipart.com is, of course, the recurring fee. Unless you have a very regular need for clipart, the costs can build up. $160 per year is a lot less than hiring artists and designers to provide you with custom artwork, but its probably outside the scope of scrapbookers and people who want to add some art to their family web pages.
Paying $15 per each week in which you want to use some clipart is one alternative, if you only need the service a couple of times per year. You are allowed to download 1,000 images per day, so you could build up a collection of clipart you think you will need.