alex@www:~/scriptaculous/$ du *.js -ch --apparent-size
This is unacceptable for just a library. Most of these KB's have to be downloaded and do not provide any functionality per-se. Broadband is not an argument here. To load or not to load 100kb is relevant.
I therefor really like the Sack of Ajax. It takes only about 4K:
alex@www:~/sack/$ du *.js -ch --apparent-size
Now this does not give us all the script.aculo.us stuff. For that case I suggest to just reuse the relevant parts of it. Just let the user download what you really use. Maybe one day we will see a reduced script.aculo.us. Or an alternative using Sack.
UPDATE: I now recommend to use protoype.js again, in a reduced version just for AJAX.