I'd say about 5. Not debilitating, but always strong enough to be noticeable in everyday life. I've read about something called "dysthymia," which is a form of long term depression that has the major symptoms of depression but with less severity. While the condition doesn't suit me exactly, it's fairly close when checking through the symptoms list.
http://en.wikipedia.org/wiki/Dysthymia
I don't consider the depression to be severe enough to warrant antidepressants (I'm not trusting of them, despite what the science might say), although sometimes when I'm really down it's tempting to think about hitting up the doc for some "woes-be-gone" pills. But I prefer not dealing with doctors unless I absolutely have to.
I tend to view depression as a major component of my personality, since I've had it from a young age. It's not bad enough to seek help, but it's bad enough to degrade my quality of everyday life.