My bad, I was actually referring to the FSA, flexible spending account. They will be capped at $2500. MY wife's employer, a hospital, issues debit cards that are loaded at the first of the year with the amount you ask for, then a portion is deducted from your check every pay period, from pre-tax dollars, throughout the entire year. It's been awesome with two kids in braces, all four of us in glasses/contacts, one kid that gets allergy shots weekly, one that needed wisdom teeth cut out and misc. Dr. visits and prescriptions. We blew through $3500 last year without even trying hard.
Yes, if you know you're going to have those expenses, the FSA is great.
If you are unsure if you'll have expenses or not, the HSA is really the only way to go.
I fully fund mine every year. I know that one day I'll get into it, and it's nice to keep Uncle Sugar out of my wallet.