All you\’re dreams have come true! 2.80 revolution (not the game) but the downgrader! Developement is currently being worked through. We had our doubts on 0okm, but hes back today to proove us wrong. But sorry folks, not only does it not work on TA-082 users, but it does require 1.50.
Heres how to install:

Quote From PSP Hacks:

1. Run moonlight’s “FW2.60 DownDate helper” on FW1.50 PSP to Dump “FW1.50 File” or Download “FW1.50 File” from psp-hacks downdater_final.rar.
Extract downdater_final.rar \\DOWNDATER\\ all file to ms0:\\DOWNDATER\\
2. Run FW150IPL_Dumper on FW1.50PSP to Dump ms0:\\DOWNDATER\\PRX\\FW150_ipl.bin
NOTE: if no FW150_ipl.bin in ms0:\\DOWNDATER\\PRX\\
Run FW280DownDate4TA-079 will brick your PSP !!!
3. Run FW280DownDate4TA-079 By xLoader
NOTE: Don’t use eLoader to Run FW280DownDate4TA-079 it will brick your PSP !!!

Downloads:
2.80 Downgrader v0.01(by 0okm, for TA-079–TA-081)
2.80 Easy Downgrader (courtesy of csfreakno1)
Sorry, no mirrors

Source: www.psp-hacks.com