I wrote this entire section on VBA to Apps Script transition quite some time ago, and of course some things have changed since then in the fast moving world of Apps Script. My new book is all about this subject and contains brand new information, especially if you are interested in VBA to Apps Script migration. You'll also find some adapted material from the book here.
First observation - it's painfully slow compared to the same thing in VBA, but see Optimizing access to sheet values. This a feature rich caching capability, both read and write, and applying to all range methods that have both a set... and get... version.
Many of these libraries are now part of a Google Apps Script shared library you can incorporate in your own project.
I have talked about data abstraction extensively on this site, meaning separating the physical data location from the data itself so that procedures are not aware of where the data is coming from, or even that it originated in Excel. This approach will serve us well, since it means that if we simply change the Data Manipulation Classes to understand about the Google Apps Data structures, the bulk of the logic will remain intact, even if they do have to be translated.
If a regular visitor to this site or the associated blog, you will know that many main functions are executed in one or a just a few lines of code, and generally speaking these avoid addressing specific Excel capabilities through data abstraction. Once the underlying libraries and classes are ported to Google Apps, it will be a simple job to port most of the Excel procedures on this site.
The Google Apps API is very powerful, and is evolving very quickly. Expect to see continued added functionality.
For more like this, see From VBA to Google Apps Script . Why not join our forum,follow the blog or follow me on twitter to ensure you get updates when they are available. Much of the code referred to here is the mcpher library. You can find out how to include it in your project here.