I have not had any issue on 5.0.1 jailbreak. I jailbreak my phone on iOS5.0.1 in early December on semi-tether using redsn0w and updated to an untethered version the day it came out on the 27th of December 2011. Yesterday, I restored the iPhone again and did a fresh jailbreak using the latest redsn0w 0.9.10b3 and have had no issues.
I restore and re-ran the jailbreak because the boot-up from a cold reboot was close to 80 seconds (I suspect because of Corona/Semi-Tether legacies etc etc). Now a fresh reboot takes about 20-25 seconds which is normal.
All my Apps are stable. I have had no crashes (except for the game Real Racing 2 which is probably because my RAM was way too low at the time) but I have not experienced Mobile Substrate crashes and have not gone into any safe mode at all.
I suggest this steps if any of you are experiencing any issues (crashes etc etc)
1. Backup your iPhone to iTunes (or iCloud, whichever you prefer) and Go to iTunes Preferences and under Devices tick Do Not Sync iPod/iPad/iPhone Automatically.
2. Fresh restore your iPhone (Do a Shift + Restore via iTunes which would require you to download the full 790MB 5.0.1 IPSW
Download Link for All Firmware Files ) This will wipe your iPhone clean and install a fresh firmware into the iPhone
3. Set your iPhone as a new iPhone (don't restore as yet)
4. Jailbreak your iPhone using redsn0w 0.9.10b3 (
Link to Download versions of redsn0w)5. Set your Lockscreen Auto-Lock to "Never"
6. Open Cydia and WAIT for it to FULLY load all the repos (this can take 5-10 minutes, yes that long). If the loading fails, exit Cydia and re-run it (you can reboot or re-spring). If it does not load automatically, go to Changes Tab and press refresh. Wait for it to download all the lists of apps from the repos.
7. Add your repos of choice
8. Wait for it to load
9. Install your favorite tweaks
Once everything looks okay and the phone seems stable
10. Connect to iTunes
11. Restore your backup to get back all your Contacts/Calendars/Settings/SMS/Game Saves/ etc etc etc