Great info from TGB above.  I'll add that I would encourage them to make an additional HSA contribution by 4/15 and take the extra tax deduction.  If covered for all 12 months (or even covered under the "last month" rule) then $3,600 limit - $2,150 payroll contribution = $1,450 available contribution.  If they can spare the cash it doesn't get any better than triple-tax-free.

My recommendations in terms of ordering of savings:
1) Max out your employer match 401(k)
2) Max out your HSA contribution
3) Keep running the 401(k) up to the deferral limit

Rick