Except the system, kernel upgrade when the restart is required. Are there any other reasons to use or not to use the hibernation?
I don't use the hibernation, because i fear that it'll bring me troubles.
When hibernation works, it works. If it doesn't work, then you just reboot. It is effectively the same as not using hibernation in the first place.
The usual caveats apply, you should make sure you don't have any unsaved work, and be aware if you have files open from a network that might not be there next time you wake up the pc.
My suggestion would be to use hibernation unless you have troubles rather than not using in case you have troubles.
I appreciate the faster boot time from hibernation. Occasionally, the system doesn't come back, but a hard reset fixes that. I usually close most applications (except mail and iTunes) before hibernation to ensure I don't lose anything in the event of a failure.
The only problem I've had with hibernation is many update programs launch on system startup. The don't launch after hibernation, so I often don't see updates until hibernation fails. For this reason, and as a general system refresh, I do a full shutdown once a week.
I've never had a hibernation failure cause more trouble than needing a hard reset, or in some cases, two.