So the first thing I did was try it out on my Treo 700p. It kept on giving me the error "does not support this filetype?" So I did some digging and found a gmail groups discussion where other Treo 700P users were having the same issues.
The instructions were posted. Basically, I needed to install IBM Java JVM onto my Treo via hotsyncing. Then after it was installed, I needed to manually soft reset the Treo by clicking on the button under the batter cover. After that, I was able to download and install the Gmail Mobile client.
The client itself works nicely. No complaints there. Good job Google.
Forum discussion at WebmasterWorld.