I recently jail broke my iPhone 4S, I used ChronicDev's Absinthe tool on the day it was released. The jailbreak didn't go that smoothly as I had to attempt it a few times and when it did finally complete I had a blank icon (white icon), for me the app that had the blank icon was the Phone app, everything still worked but it was ugly and annoying.
I lived with it for a few days because I was busy but eventually decided to try again with the jailbreak. A couple of days had passed and ChronicDev had released an updated version of Absinthe, version 2. I had done a bit of reading to try and find out what might have caused the blank icon issue and there wasn't much info available.
I decided that I would backup my device (very important), restore to stock 5.0.1 and then do the jailbreak on the clean phone before restoring from my backup. I did this and when the jail break finished this time I had a blank Maps icon - arrrggh! One thing I had seen on twitter (and as a message on Absinthe!) was not to touch the device while the jailbreak was in progress, however each time I hadn't been able to resist unlocking the phone after the first reboot, this was because a device passcode (not SIM passcode) can cause the jailbreak to fail.
3rd Time Lucky...
I decided to try one last time, so I restored to stock 5.0.1 again (without loading all my stuff and settings back on to it - so no device passcode lock) and then ran Absinthe 2 again. I clicked the Jailbreak button and then stepped away and made myself a coffee, buy the time I got back Absinthe had finished and all that was left was for me to run the new Absinthe app that was on my iPhone (or go into settings and toggle on VPN). At this point I was already confident that this time was a success as none of my apps were blank so I opened the Absinthe app on my phone and after a few moments the phone rebooted and when it came back online there was the new Cydia icon on my springboard and best of all no white icons - yay!
After that all that was left was to load up iTunes and restore from the backup I had done earlier. The backup restore and then a sync and everything was back to normal and it was off to Cydia for some tweaking.
I hope this helps some of the other people that had the blank icon issue as there really was nothing useful about when I was trying to find a solution.
Also one last thing, if you are going to follow the above and try and fix your blank icon issue then make sure you do it before Apple close the signing window on 5.0.1.