Since you did have an account at Mt. Gox and there is an ongoing class action suit, I would send them an email or give them a call to see what is involved in being included. I am not a lawyer but I imagine that the potential upside of signing up outweighs the potential downsides (risk of countersuit is probably negligible, for example).
The obvious calculation will be:
How much your time is worth * how much time you need to invest in getting involved in the lawsuit
vs
(the value of your BTC there * the fraction you could reasonably hope to recover) - the fees of the lawyers.
Best of luck; hope you didn't get hit too hard.