It took a minute to load, brought my beefy laptop to its knees and every character key press takes half a second to display... Probably the most faithful recreation of the Smalltalk I used to use in the late 80s.

Either your 'beefy laptop' isn't so beefy or you're exaggerating for some odd reason. On my four year old iMac (and we all know macs are soon slow by comparison to real computers, right?) it took 15 or sec to load (which is almost all network time) and typing could handle the fastest I could hit keys.

Someone broke that page (it's a Lively page, meaning it's editable by anyone). Here is a stand-alone version, running ThingLab: http://www.cdglabs.org/thinglab/