Gtoolkit [1] is a cutting-edge example of what's possible. I say "cutting edge" because it relies upon a dev version of Bloc, which is the new graphics system being developed for future versions of Pharo.
Any sluggishness you experience with Gtoolkit, by the way, is because Bloc is being hosted in Morphic (the current graphics system) temporarily.
There is a ProfStef object that you can send a message to (can't remember the message, maybe "go") which runs through a decent tutorial. After that I'd download one of the books and start going through that. I'm only a novice (have read maybe 1/2 of a book and played around in the IDE a bit). Pharo is really cool, but my programming needs are scientific in nature where I need something closer to Julia where there is a lot of builtin support for numerical work. Someone did write a numerical methods book in Pharo which was neat, but it is still lacking the libraries I need.
Any sluggishness you experience with Gtoolkit, by the way, is because Bloc is being hosted in Morphic (the current graphics system) temporarily.
[1] http://gtoolkit.com