How does the list of proposed services map to the vision/strategy/etc. of the enterprise? It can be revealing when the proposed list of services are very low-level, very fine grained, but the project claims a close alignment to the enterprise strategy.
Who are the participants in the services? This often gets at the fact and the fiction of re-use. A popular tactic to garner support for a project is a claimed level of re-use but it is a good idea to identify who (if anyone) has actually signed up for the offered service. Conversely, many project managers support the idea of enterprise services to avoid a "reinvent the wheel" situation but taking a capability of an individual project/product/etc. and making a service that others can use comes with it work, expense, commitments, that the project may not want to take on.
How are services created, evolved and eventually retired? Services don't necessarily have to come from new development. They should be designed to age and degrade gracefully. The enterprise development processes and technical architecture need to provide a deprecation/retirement mechanism.
How are the current (not service oriented) development processes working out? If the enterprise is struggling with the basic development mechanisms (requirements management, testing, configuration management, etc.) while still working in a project/program mode then they are in for a big shock trying to take on enterprise services.
What about the money? This is a common deal breaker. Everyone wants to re-use the services of someone else - not as many people want to take on development of a service for the rest of the enterprise...especially with little or not adjustment to their budget. In may enterprises the funding model works against services because by law, regulation, or policy the money goes to distinct projects - funding a service under these circumstances can be difficult....even illegal. Constructing effective financial incentives is one of the most important, and often overlooked, mechanisms for attaining effective enterprise services.