I have been a big proponent in the past of Unity and Dependency Injection, especially related to aspect oriented programming. Allowing automatic transaction and logging support are two key areas where AoP has provided huge benefits to the simplicty of application development.
With a caveat that this works really well for atomic systems, where a request is self contained and all the necessary processing occurs in the one transaction.
Some limitations of this have arisen during the design of the Market game however, and this is predominantly due to the need to inject 'time' into the equation. Ultimately we are attempting to perform an action that spans a period of time and during that time we may wish to read the progress of that task. When a task is a single transaction however, it is not possible to read that progress from outside the transaction. This leads to the scenario where we need to perform a method with custom transactional scoping. i.e. do it manually.
This introduces room for errors, because we need to ensure that it is not possiblle for a UnitOfWork method to call a 'manually managed' method, as this will corrupt the UnitOfWork scope, and the same for manually managed methods calling UnitOfWork methods.
We also need to ensure that for a particular service instance we can't call a second method while a "long running" method is in progress, as the DbContext scope will be affected (since it is shared between instances of the dbContext). This is actually a more general issue, you cannot reuse a Service instance if there is an on-going action.
Yes this can be worked on, and is not a very difficult change to make, but it does mean that there is the potential to introduce 'unexpected' behaviour, which is one of the reasons AoP and dependency injection is so useful.
Finally, as for my Market Application, I may rethink my concept of Time. This is something I've been looking at for a little while, and it does make sense. Basically it is changing Time to be more like the facebook game model. Essentially everything the user wants to do will take up X Action Points, which can be gained in a number of ways (time being the primary one).
This would resolve the issue we have with "Actions taking time" as every action would be immediate (if you have enough AP), but you just can't do anything else until you have more AP.