Didn't see a specific thread for it so here it is:
(I remove corrupt and and start-up boot, and start up boot removal causes most of these errors.)
Unable to launch 1.5 FW from Flash
Related to top, but this makes devhook unable to run 1.5 stripped ISOs(gray area legalish back-ups)
Running other firmwares with a UMD in the tray(XMB reboot) freezes the PSP after gameboot loading of UMD/ISO(Fix-able by not having a UMD in when launching the firmware).
Going into the 1.5 flash XMB from 2.6/2.71 firmware shortcut causes it to go into recvovery mode(fix-able if you change the recovery eboot source to only listen for L[or R, forgot] and not launch if other buttons are held).
Many programs fail to launch unless you put their folder files onto ms0: (Eboot copying and then the eboot not finding it's related files...?)