As you have probably read, the US Atty. for the SDNY has issued a subpoena for Mt. Gox Records according to news reports.
If you had an account at Mt. Gox last year, and if AT ANY TIME DURING THE YEAR the account value exceeded 10k, you may want to file a foreign financial account form - called a 90.22.1 form (also known as FBAR). Remember CoinDesk reports $1,147.25USD per BTC on 12/04 of last year as the highest value for BTC - Gox was likely higher and is a safer number to use but their site is down.
I have seen nothing on what was requested in the subpoena. Subpoenas are typically not made public unless released by the individual or corporation who received the subpoena. I also don't know who was the entity the subpoena was issued to - Mark personally, Tribane, Mt. Gox LLC, the US subsidiary that was subject to the seizures last July, Mutum Sigillum LLC or some other Gox-related entity.
In the meantime, all the more reason that you consider filing the forms..... and presume your account and trading information will be turned over.
Link for info and form is below. The penalties for not filing are hefty. If you had several accounts at Gox I suspect they will be looked at as if they were a single account...
http://www.irs.gov/Businesses/Small-Businesses-&-Self-Employed/Report-of-Foreign-Bank-and-Financial-Accounts-FBAR