I'm trying it on a small project (300k LOC - 1033 java files + 367 ui files + 67 GWT-RPC services) and takes 539785 ms to compile every time I hit the compile button. The old dev mode takes less than 5s to refesh the page.
Compiling module pt.ipb.rad.RAD
Compiling 1 permutation
Compiling permutation 0...
Source Maps Enabled
Compile of permutations succeeded
Linking into /tmp/gwt-codeserver-857158151847711909.tmp/pt.ipb.rad.RAD/compile-1/war/rad; Writing extras to /tmp/gwt-codeserver-857158151847711909.tmp/pt.ipb.rad.RAD/compile-1/extras/rad
Link succeeded
Compilation succeeded -- 538.911s
Compile completed in 539785 ms
Fedora 17 x86_64, core i7, 8GB RAM