I was giving feedback on a seminary assignment and thought I would copy some of what I wrote here.
I believe Luke-Acts was written after the destruction of the temple in AD70 because:
1. Almost all experts have concluded that Luke drew on Mark as a major source, and most experts date Mark either to the late 60s or the early 70s. Luke-Acts would thus have to date later.
There's a whole lot of thinking just behind that preliminary paragraph. For example, there is the synoptic question, the fact that Matthew, Mark, and Luke are so similar on a verbal level (although sometimes with minor variations) that it is a virtually unanimous position that the three stand in some relationship of literary dependence. Most think Mark was first with the others later. A minority think Matthew was first and the others later (I reject this position because Matthew's text is grammatically smoother than Mark, and it makes no sense that Mark would "rough up" Matthew's). But I know of no one who thinks Luke was first.
I'll leave it at that. One thing I'd like to push here is that most pastors have no idea how much minute examination of the biblical texts has led to these sorts of conclusions--or how much support they command among those who have done the homework. It is a disconnect seminary would ideally connect, while letting you come to your own conclusions. In any case, if Mark reached its final form not long after the destruction of Jerusalem (as I think) or even if it was written in the late 60s (as others think), it would place Luke-Acts later, likely after the destruction of the temple.
2. One example of the kind of painstaking and detailed work is when you compare the readings of the individual gospels and look for signs of how the theology of a particular gospel writer impacted the way they edited their sources. For example, when we compare Mark 13:14 with Luke 21:20, we see some clear signs of Luke's editing. Mark and Matthew both have the very ambiguous, "When you see the abomination that causes desolation standing where it should not be..." Luke's version is quite different, "When you see Jerusalem surrounded by armies, you know that its desolation is near."
Could Jesus have said both? Sure. Not likely. This is not a parable Jesus told over and over again. It is an explanation at a particular place and time. And when you have compared the gospels over and over again, you inevitably come to grips with the fact they are using each other and you accept that this is overwhelmingly likely to be Luke editing Mark. Again, there's no substitute for the long, painstaking comparison of the gospels if you really want to understand how this sort of thing works.
So notice how different Luke's inspired "Message" translation of Mark is. In Daniel 11, where the abomination language comes from, we would think it is the temple being desecrated. Matthew and Mark can easily be interpreted this way. The abomination is standing somewhere--in the temple in Daniel. To see it as armies surrounding Jerusalem is not what we would have expected.
In short, Luke's editing has all the marks of an explanation of the prophecy with the insight that comes from being after the events, after the destruction of Jerusalem in AD70. Mind you, I think Matthew is post-70 as well and it doesn't make these changes. But making such edits is part and parcel of the way the NT interprets the OT. Again, long, detailed examination of these patterns leaves us with this sort of strong impression.
In short, I find it very difficult to think of any open-minded way of arguing for a pre-70 date for Luke-Acts. Certainly if one is determined to argue for something, it is almost always possible to do so. In my mind, however, a true scholar of the Bible is someone who looks for what is most probable, not someone who applies their intellect to defend the possible but more convenient!
My opinions. You are welcome to disagree!