I almost never shut it down. Probably only once a month.
Waking from sleep is faster and I don't have to re-open my applications and documents. Shutting it down would save a small amount of power but that's rarely an issue (I'd shut it down if I was flying somewhere).
Are there some benefits to shutting it down I'm overlooking?
If you suspend, you are vulnerable to reading decryption key from RAM (firewire, ram freezing). If you are doing full disk encryption, then only shutdown or hibernate are secure.
My encryption key doesn't live in RAM because I use TRESOR. It's hidden in the debug registers of my CPU. There is still going to be other sensitive information in RAM though which I wouldn't want to be accessed.
With SSD, on OSX, it's pretty fast to reboot. Most OSes can now be tuned to boot very quickly; the big thing was getting rid of the BIOS for EFI I think.