The hacks are pretty simple to do and it's not like hacking other devices, you can reflash it with sony's firmware and I haven't heard of anybody bricking their device because of these hacks.
I like the clock.
I put better font on it. ... its' bolder and the one the people in the forum room recommended as the best because it fits the dot pitch and size for the screen. It offers more contrast for me since font looks darker.
I also used the ONE button turn off hack , I hold the PAD button 5 seconds and unit turns completely off. It beats having to go into 4 or 5 pages of menu's to turn it off.
I like making the history forward key the next page button too.
p.s. I forgot one last hack , CONTACT hack , ...you can put your name , telephone number, and email address on the unit, and if it is lost , people can contact you. If police recovered it , they could contact you. And if you had to prove it was your unit, you could show them it has your name on it!
Even if some bad guy took off all the books by deleting them, your name is still on it and he couldn't take it off!
Now if this unit came with built in lo-jack, that would be better , but something is better than nothing.
Those are the features I'm using from the hacks , and maybe others will post the ones they like too. if there was danger of ruining the 505 , yeah, I might caution there use , but I don't see any downside and if you guys can come up with one , let me know.