General

There are several different types of lag. The most common type is internet. To further understand how your problem works is to understand Server and Client. The player is the Client, lag on our end would be poor internet connection and/or speed. Usually seen when several people are on the same internet connection, your bandwidth speeds will drop since you are sharing the one connection with someone else.

If that is not the problem, you are able to take the next step to addressing the issue

Server - This is what the Client connects to in order to play Maplestory. Nexon provides the servers and infrastructure designed to host a wide majority of players. However, the server can develop slow response speeds as well, due to a vast group of players drawing on the one server. Think of 5 people sharing a 20 oz drink. Each person is pulling on that one drink and it will empty quickly. Therefore you have to get a bigger drink in order to satisfy each person to reasonable expectations. Nexon, therefore, would need to increase their infrastructure to satisfy the player base. It just so happens they released a major patch so more people will be drawing off of the servers. Once the hype dies down, you can expect performance to increase since some of the people who were only on for the skill links or equipment got what they want.