I am not sure whether the $25k limit before the IRS comes after you for tax debt includes interest and penalties. If so, then you'd need to underpay less to avoid having the IRS come after you. The underpayment penalty is ½% per month up to a maximum of 25%, plus interest at a rate of the federal short-term rate plus 3%, determined quarterly. I am trying to clarify this ambiguity and will update this thread.
[EDIT: the $25k includes interest+penalties; see thread addendum.] (9/11)