Part of the "S stands for Speed" boost in the iPhone 3GS' bullet points is support for faster HSPA 7.2Mbps data transfer. The giant honking asterisk at the end of that sentence, however, is usually "where supported by carriers, real-world speed will be epically slower".
So, real world TiPb community, just how fast is your new iPhone 3GS? I posted a few results above for what I'm getting on Rogers in and outside Montreal. Let us know what carrier you're on, and what speeds you're averaging?