At our house we have an agreed upon policy - if it's over $200.00 and it doesn't involve groceries or staples - then it's up for discussion. What constitutes a large purchase at your house?
When we first got married we agreed on something pretty much along the lines of what you have said, except we put the limit at $100 instead of $200. Four+ years on that has definitely morphed into a more lax rule. Generally speaking though we are each aware of what the other does. If we go to clothes stores, we know that the other is going to spend money, even if we don't clear the exact amount at the register by the other before purchasing.
We also each have a "play money" account that we can spend on whatever, no questions asked, no need to check in with the other partner. Those accounts don't get used too much, but it is nice for the occasional whimsical splurge or for purchasing gifts for the other person.
Also: this is odd, but I tried to post my reply and the USSA website wouldn't let me post a phrase with the word that rhymes with "hopping", starts with an "s", and means "purchasing". Strange sensors/filters they are using...