As there are increasingly more than a few folks between opportunities these days, I thought I would put forth some thoughts on how to evaluate a job opportunity with sort of a "due diligence" check list. 

Scoring high or low on the criteria below is not necessarily good or bad, but will help clarify the true nature of the opportunity in front of you.  Also, this definitely has a technology/early stage bias but can be abstracted to other industries and company stages.

• Defined market – Target buyer(s) defined, validated, and the way(s) to reach them known and proven?
• Defined product – Aligned with the strategic landscape and market needs?  Are different customers on different code bases?
• Defined pain or process with proper domain expertise – Known "problems solved" with sufficient resources on staff with credible domain expertise in the problem space?
• Defined sales path – Existence of a predictable, repeatable, and dependable process for finding, engaging, and closing customers?
• Stable team in proper geographic concentration for stage of business – High caliber, intellectually invested, long serving team?  If any of the above bullets are lacking, all execs should be in the same office.
• A track record of success – Reference previous post on turnaround vs. growth opportunities.
• Strong, referencable customer base – Strong business relationships in addition to service/support.  Is the company viewed as an adviser as well as a vendor?
• Mentorship/professional development – Emphasis on setting people up for success, respect for each team member and a strong meritocracy?
• Authority & ownership – Amount of leeway and decision making granted about spending, hiring, external communications, etc.
• Financial stability/committed funding – Cash in the bank, burn rate, milestone-based additional funding vs. committed, existing timeline for exit/sale?