UPDATE: I've made a few clarifications

In our Greek readings class we came across Matthew 5:48, which reads:

εσεσθε ουν υμεις τελειοι ωσπερ ο πατηρ υμων ο εν τοις ουρανοις τελεις εστιν

This is usually translated "Be perfect, just as your heavenly Father is perfect."  While this is a possible translation, the verb εσεσθε is actually morphologically a future tense verb.  This can be used in a jussive sense ("you shall be perfect" - simplified to "be perfect"), but I think the context may be indicating that we treat it just as a straight future.  In this case you might read it as "then [i.e. if you do this] you will be perfect, just as your heavenly Father is perfect."

I think the key to this is Matthew 5:45, which tells us that God "makes his sun to rise on the evil and the good, and sends rain on the just and the unjust".  This is in the middle of a whole description of action in which Jesus said that we aren't just to do good to those who do good to us, but to others as well.  Give to those who ask, even if they can't repay.  Love those who hate you.  Pray for those who persecute you.  Greet people who you don't know. 

It is obvious from the state of the world that bad people can have it good.  It sometimes seems that evil people are blessed by God.  In fact, it may so happen that they are!  As these verses indicate, part of God's perfection is that God blesses those who hate him.  God blesses those who are just and unjust.  God blesses those who use that blessing against Him.  It is part of His perfection to do this.

And so, at the end, Jesus is saying that if we treat others the way that God treats them, we will be perfect.

This solves for me a moral problem and a theological problem that I've wondered about for a while.

The moral problem:

• If I sell products or services, should I sell them to evil people as well (provided it doesn't require me myself to do evil).  Answer: Yes - God gives to the good and evil, so should we.  For instance, it would be fine to be an accountant for an abortion facility.  It would not be fine to do the abortions.  Also, being their accountant would not mean that you are to be silent on the ethics of their operation, just that you wouldn't withold services on account of them practicing evil (interestingly, I am aware of one abortion doctor who was converted because of his accountant and then stopped doing abortions).  Now, especially for those in the services (as opposed to products) industries, there is the whole question of time allocation - since you, unlike God, cannot be in two places at once, perhaps you may choose to not render your services to some group or other.  I think that this is your own choice, and it depends on what God has called you to do.  However, I don't think we should necessarily withold our services when someone requesting them is corrupt or immoral.
  

The theological problem:

• Why are there so many people who hate God but appear to have God's blessing?  Answer: Because God gives to the good and the evil

Now, the problem that it adds is whether or not those who have taken God's name and received His Holy Spirit also receive more than those who do not (by more I do not mean material possessions).  I think the answer is a qualified yes.  I think that by receiving God's spirit and submitting to God's will then our gifts will be used for God's glory, in consonance with God's purposes.  It also means that we know to ask God, while those who do not know God do not know to ask.  There is probably more here, too - this is not the whole story, it is only one part of the Bible.  But the point is that God does in fact give to both the righteous and the unrighteous (and takes aways, as well).

I think we need to stop translating this as a jussive/imperative and just make it future tense, because it makes better theological sense of what is going on.