Yesterday, there was at time where I lost 4g for about an hour. I didn't notice at first, but a reboot took care of it. As far as switching for me, all is fine going from 3g/4g/WiFi.
This is what I did when I installed it. I was on the MR2.5 radio Sense 3.0 Preview 4 at the time of install.
Reboot Recovery
Wipe Data/Cache
Format System
Install Alpha 2
Reboot phone
Connect WiFi
Reboot recovery
Flash Gapps
Sync Gmail
Battery Pull (boot into bootloader)
Flash Stock radio
Reboot
Turn off WiFi (connected to 3g instantly)
Set my phone up
Hope this helps people.