Ladies: how many bras do you really need?

Ok I realize I'm the exception and not the norm, but I kind of only own one bra at a time and then replace.  My bra gets washed once a week and I work a normal desk job (so not a lot of sweating going on).  Basically the minute I get home, the darn thing is off and I'm in a comfy tee and some shorts.  Now I may be kind of a hippie, but I don't like bras.  I mean - we all have breasts, what's the big deal?  After the birth of my son, I got even more blase about it because (let's face it) those girls are never going back to their prim & proper state after breastfeeding.

After reading some recent articles it seems the norm is five bras:

• One "fun" bra
• Two everyday bras - most common colors nude & black
• One convertible/strapless bra
• One sports bra

However, it would appear that on average at any give time women can own up to 16 bras at a time and buy about 4 new bras a year.  Apparently we'll spend roughly $4,000 in our lifetime on (you guessed it) bras!

Back to the above list - to be fair, I do own a sports bra and a nursing bra, but I don't own a single strapless bra.  Underwires are so uncomfortable to me.  Can you tell I'm a tshirt and flip flops kind of girl?  I don't much care for high heels either (especially chasing my  2 year old around ...).

How many bras do you own?  Any advice for me to expand my collection?