The first thing that I think we need to look at in Jude is divine and human judgment. Divine judgment is a major theme of this short letter, and it also raises interesting questions related to human judgment.
The first thing that jumps out at us is that God judges sinners, and Jude brings up several examples. As we know from the Old Testament and 1 Enoch, Balaam, Cain, Korah, the wilderness generation, Sodom and Gomorrah, and the fallen angels are all judged by God. God will judge sinners, and not only does he judge all of these sinners, but when you read their stories in the OT (or 1 Enoch) they all receive at least some judgment here and now, prior to the final judgment.
While with some of the examples the judgment is blatantly obvious (e.g., Korah or Sodom and Gomorrah), for some you must know their story to see how God's judgments works out. If we did not know the story of Exodus-Numbers we might have thought of wilderness generation as a random nomadic people and would not have known that their extended sojourn in the wilderness that ended in the death of the entire generation was God's punishment. Thus, from the perspective of the outsider, God's judgment on someone may not always be obvious. Conversely, when we look at the story of Sodom and Gomorrah, many of the people probably had no clue what was happening to them as the God's wrath (literally) rained down on them. Thus, the people being judged by God may not even realize that God is judging them.
I would like to propose that the overall thrust of Scripture, including Jude and the OT examples he cites, suggest that God does judge sinners here and now on the earth. We may not always realize when others are punished, and they themselves may not realize it, but God's wrath towards sin and sinners continues to operate here and now, on this side of the second coming. Jude seems to imply that the coming of the cross does not usher in a new era when God only pours out love and mercy and never shows wrath.
What about human judgment? Clearly some judgment is allowed, because Jude does denounce the false teachers and their ways. However, we must note that in every OT case cited, God was the one who meted out punishment. The story of Cain is worthy of attention. Cain was worried that not only would he face the punishment of God, but that humans would mete out justice on him too by killing him. What does God do? He allays his fears and guarantees that no one will harm him. Carrying out punishment, in this story, belongs to God alone.
Like in the story of Cain that Jude cites, it's noteworthy that Jude does not direct the church to mete out any punishment on the false teachers and those who follow them. The emphasis is on restoration. It helps balance out a somewhat unbalanced reading of church discipline texts of some. Church discipline texts like Matthew 18:15-20 are not, 'the steps to excommunicate someone.' Rather, they are steps to hopefully restore someone to fellowship, with excommunication being a last resort, and even that being done with the hope that they will return repentant. Jude is all about mercy toward those who are straying, specifically a mercy that does not condone sin, but confronts it hoping to see repentance.