Recently found one thing. Perhaps in docs for AJAX client or somewhere else was such line:
Sys.Application.notifyScriptLoaded();
You need to write this line at the end of your JS files. But this can cause the problems if you wish to re-use this code in non-ajax enviroment. For this better to use following line:
if (typeof(Sys) !== 'undefined') Sys.Application.notifyScriptLoaded();
This makes things a bit better. Also, it answers another question - "Testing for defined variables in Javascript". Sometimes I see the code like:
if( Sys )... // And this will fail in case Sys is undefined.
That's all for now, it's summer. Everybody enjoy their resort life. But I'm still working.