It looks like downgrading to 1.5 won't be necessary for much longer. A WiFi demo's been successfully loaded via a constantly updated eboot loader
for firmware version 2.0, an achievement which isn't just a feat in itself, but also leaves more room for the eventual appearance of other homebrew apps for PSPs running the firmware. A homebrewer named Fanjita, along with a crew of code jockies, made the announcement today, and included a detailed guide to getting the demo to run. They admitted the exploit wasn't pretty to look at, but damn, it at least makes a strong impression.