Hi cdorob,
Welcome to 5 Star. I've seen you reading my blog through MyBlogLog.
Thanks for starting off with a great question.
"What affiliates should check about an Affiliate Program before signing up?"
Check for commission leaks - Leaks are ways merchants can siphon off the traffic you send to them - so they get paid but you don't.
Common leaks are merchants that run Adsense on their site. Adsense causes the visitor to click off the merchant's site - then the merchant gets paid for the click but you get nothing. Other leaks inclide 800#s if the merchants does not have 800# affiliate tracking set up, links to other affiliate programs and ad banners.
Check merchant site for conversion issues - If you find multiple merchants offering the product you want to promote, then evaluate how user friendly the sites are and compare ther prices. One may pay higher commish but if that merchant converts poorly you could make out better with the merchant that pays less but converts better.
Who's next? What else?