There are several inter-related to answers to your question.
- The vast majority of your application's code is cacheable by the browser, meaning that it will take some time to download the first time, but browsers should be able to cache it thereafter.
What these points come down to is that while GWT apps can easily get into the 300KB+ range, GWT tries very hard indeed to keep file sizes small. We frequently compare the output of GWT to the output of hand-written equivalents, and GWT almost always wins. In cases where it doesn't win, we examine why and try to improve the compiler.
Additionally, in the upcoming 1.4 version, we have several compiler enhancements that will do some incremental improvements to reduce output file size even more.
I realize this is not a simple topic to get your head around, but I hope that helps!
- Dan Morrill