This won't be relevant to everyone but I know some computing students read this blog so for their sake I'm embedding this very good presentation on "The art of doing a PhD".
My synonyms for PhD: hard, lonely, exciting, humbling, exalting, confusing, interesting. And most of the time you have no idea what you're doing, but Einstein said it wasn't research if you did, so I guess that's ok.
I'm glad to be at the end of it now, and I have to say that any work experience you can get during your PhD is very valuable. Coming out of University at 30 with with no work experience won't impress anyone. Show you can walk the talk.
I'm a phd student in Computer Science, and I work in seo as well. I've DJed for 5 years (now just for fun) and I've been dedicated to Ashtanga yoga for 4 years after a long stint in extreme sports. My favorite word is "orange".