Hello all!
I have written this to explain all about the update, the new launcher and more. Lets get a few thigns straight.

• A new minecraft version 1.6.1 has come out.
• There is a new launcher that allows you to play previous versions and have multiple minecraft.jar's in essence.
• You can update and still play ECC, which I what I will explain now.
• You can still keep all your mods and setting, I will explain below.

Right I will give you a step by step guide as to how to update minecraft, keep all your mods and still play ECC.

• Go to minecraft.net and download the new launcher.
• Go to the .minecraft folder, then copy the minecraft.jar from the bin folder and paste it to yoru desktop
• Execute the new launcher and let it run.
• Close it then go back to the .minecraft folder.
• Open the versions folder and create a new folder, for the purpose of this tutorial I will name it "1.5.2 Modded"
• Cut and paste the minecraft.jar from the desktop to the "1.5.2 Modded" folder.
• Return to the previous folder called "versions", open the 1.6.1 folder and copy the JSON file.
• Paste the JSON file to the 1.5.2 Modded folder.
• Open it and edit the first line with the below
  "id": "1.5.2 Modded",
• Save it then open the launcher.
• Click the new profile button and name it whatever you want, then under the version select "1.5.2 Modded".
• Then login and play.

If this guide it a little confusing, which it may be, watch the youtube video below. Though it does not show how to do it exactly it may give you an idea of how to do it.

 

Well it is kinda relevant in general as well, I put it in general so more people would see it.

 

The new launcher allows you to play every version, play a modded version and a vanilla version and more, it is simply more convenient, anyway I just pulled it together incase anyone did not know how.