I don't very often, since I have a notoriously black thumb, and lack the means of getting certain dried flowers.
Sometimes if I feel it's necessary I use dry herbs in spells, but normally I use them, or would like to use them, more for crafting items, such as a door wreath/swag for home protection, and I like to keep flowers in my house to help me feel more connected to nature. Sadly the lack of natural light kills my plants, and I have this amusing notion of myself as "murderer of houseplants".
I'm trying though.
I'm trying to learn more about herbalism in general, both magical and mundane, including a hefty dose of kitchen and hedge witchery, even though it's not exactly "traditional" (well, not traditional for a recon, anyway).
I got this cool program called "HerbMasters", which is a (non-pagan) program about herbs, how to grow them, which are edible, and which have what medical/healing properties. It's incredibly comprehensive.