Andreas Raab wrote a nice primer on profiling in Squeak. MessageTally might be the single most undervalued Squeak performance tool - a mandatory read for every serious developer.
Lately I work on Squeak integration in the One Laptop Per Child ( OLPC ) project, perhaps better known as the "$100 laptop". The whole etoys group came over to OLPC's office in Cambridge. Squeak looks surprisingly well on the display prototype, and also etoys are reasonably fast. Ian Piumarta took some nice pictures , which might very well be the first photos of the actual display in the wild.