I love Freelance Switch all the way around - such a great site.
While looking for other info I ran across this really interesting Client Analyser tool. Enter in the number of clients in your cache that you wish to analyze, then fill in the specific details for each like: how many referrals they sent in the last year, how much income resulted from that client in the last year, how quickly they pay their invoices, etc. etc.
The tool helps you see which clients are 'high maintenance' and which are helping your business grow.
Check it out here.