Why not? It fixes all of the following things that people have long been asking for and has a lot of exciting new features providing very compelling reasons to upgrade the applications using Jet 3.x or Jet 3.5x Replication:
Removes "Data Errors" from the product so only conflicts exist, of which all can be deleted, and thus you are never left with data errors that cannot be resolved.
Allows you to do tracking at the column level, instead of the row level, so that if multiple people edit the same record, but not the same columns, you can avoid having a conflict. (You can also keep row-level tracking if your app needs it).
Reports conflicts at ALL replicas instead of just the losing one, which allows you to create centralized conflict management schemes. You will never lose conflicts as in prior versions.
Better internet synchronization that allows you to work through firewalls and allows you to modify a lot of the previously hardcoded params, like timeouts, so you can make your app more robust.
Better conflict management, which works on a priority basis instead of the lame "most updated" scheme. It's so cool I do mind losing the laugh I used to get telling people about the old scheme at conferences. :-)
Better conflict tracking with lots of new fields to help you better understand why the conflict occurred, who it was with, and how to fix it! This means better custom resolvers!
Child conflicts! A good example being if you do a dupe primary key of two customers. There are no more errors, so what Jet does is delete one of the customers and puts them in a conflict table. But what if they had Orders or OrderDetails? No problem! They are deleted too.... but by using the new conflict tracking, you can tell that these conflicts are "children" of the original conflict, so you can automate resolution based on what you do with the main conflict in Customers, or have some sort of custom logic, or anything!
The TSI Synchronizer has a 4.0 version that is wonderful (the 3.52 version was written after the 4.0 one), and is already available! So, Replication Manager is not something you need anymore!
Well, thats enough for now. If you are not excited by any of the above items it is clear you have never used Jet 3.x or 3.5x replicaton. These new features alone make for a very compelling upgrade for apps that use replication.