Personally I'd like to track the following (roughly in order of importance):

• MRR (monthly recurring revenue)
• Total number of paying customers
• Total number of featured startups on BetaList (very specific to that product obviously)
• Total number of products on WIP (also quite specific)
• Launch of a product (although we now have /launch for that)
• Launch of major new features (maybe this should be a separate feature though similar to /launch)