When I rolled over my 401k to my new employer I let a loan default, did they take out the 10% penalty when I got my distribution check or do I still owe someone?

Well, if the rollover amount is 90% of what you thought you were rolling over, then they took out the 10%. How much were you expected to rollover and what is actually in your rollover account now?

The 10% would NOT have been withheld. Did you receive a 1099-R from the 401(k) plan? On it you should see the amunt of the withdrawal (the loan that defaulted). The amount of tax withheld I'm guessing is $0 - since this was a loan - but again check the 1099-R.

You will need to include the withdrawal as income on your tax return (line 16 - "pensions and annuities"), and show the 10% penalty on line 58 ("additional tax on IRAs, other qualified retirement plans, etc").