I just found out from my sales rep in the Olympia regional office, that Esri does not plan to support the Google Map V3 API. The V2 API has been deprecated since last May. I think this is a huge mistake. It also seems very protective and short-sighted on their part. I�??d like the user community to weigh in here.
Google and ESRI are in some kind of GIS power struggle. I'm not sure what it's about. I suppose you could find some answers on the internet. I asked an ESRI rep about it at a class and the very question made him uncomfortable. You will note that the ArcGIS JS API can consume Bing's map tiles. This is how I see it; ESRI and Microsoft are friends while Google and Microsoft aren't, and all of them are tech giants. Draw your own conclusions.
ArcGIS Extension for the Google Maps API is simple and beautiful, however it has some limitations. Concerning GMaps v3, the API itself has changed to MVC and is hard to work with for in-depth GIS web app development. Google Code has a code library called google-maps-utility-library-v3 which can be found here. While it works well for adding dynamic layers, etc; it has some problems. The biggest one is you cannot print maps with overlays on. I suppose it works well enough for simple maps. I personally wouldn't spend a second with it, unless you like being disappointed.
I've been deploying ArcGIS Server and building full functioning web-based GIS applications for a few years now. Here's my advice: switch to ArcGIS JS API or Flex. Both are way more powerful. ArcGIS JS API is particularly powerful when deployed with asp.net instead of just html. Even better if your data is stored in ArcSDE. The web-based GIS application possibilities are endless.
But you say you want GMap tiles? You can have it. Find a library here that allows you to consume Gmap tiles with ArcGIS JS API. This is a simple example. To make it work well in a complex application you have to apply some tweaks.