There's your problem.
I attempted to install 3.0 and ran into the same problem, this is how I fixed my iPhone. For some reason Quick PWN does not recognize the iPhone when it's plugged into macs.
You can read this guide which I followed to the T and managed to fix my iPhone.
http://thebigboss.org/2009/03/19/iphone-v30-beta-do-not-use/
specifically pay attention to
"Here is a more detailed set of instructions by Max:
1) Download iRecovery
2) Place both files on the Desktop
3) Open terminal and type cd ~/Desktop
4) Run command chmod 777 libusb-0.1.4.dylib
5) Run command chmod 777 iRecovery
6) Run command defaults write com.apple.finder AppleShowAllFiles TRUE
7) Run command killall Finder
8) Navigate Macintosh HD > usr > local > lib
9) Copy the file libusb-0.1.4.dylib into that folder
10) Open a new terminal
11) Drag-and-drop the iRecovery file into the Terminal so that you get a shortcut to it.
12) Append -s to the end.
13) Run command fsboot (i had to do it twice)
14) If the phone starts up locket once again, just run through steps 10-13 again.
15) When done, open terminal again and type defaults write com.apple.finder AppleShowAllFiles FALSE
16) Then run killall Finder once again and your done!"
instead of using Quickpwn follow the instructions for the terminal stuff and your phone should be back to normal.
hope this helps.