If the forum gets hacked again, then who knows what will happen with the data which was compromised. It'll likely get sold and eventually surface in the public eyes for free.
How likely is it that the government will request your information? Unless, you are caught breaking the law and up on trial it's unlikely that they would send a request. The above link was major news around the crypto world. It's probably the biggest subpoena that theymos has received to date. If theymos does receive a request to release data on you then it's down to his discretion.
Well I don't know how likely that the government will request my informatios but you never know,we can't predit the future.
Although there is someways to hide IP address and stuff like theymos said:
I am willing to cooperate with police on real scams. Whenever someone asks me to release a scammer's IP, I tell them to have police email me from an official police address. I have received police requests a handful of times. Mostly the cases were real scams and I gave the police the requested info. In some cases I've rejected their requests. For example, I refused to give information to some foreign version of the SEC because securities laws are unjust. Of course, you should not trust that I will act in your best interest. If you want to be anonymous, then you must use Tor (or whatever).
But as far as I know Bitcointalk is blocking connections from tor and asks to pay some fee to be able to use the tor proxy IP.I guess that is to avoid multi-accounts from scammers and spammers but it's problematic.