I started out doing SEO, and I mean mostly either in-house or freelance. I switched to PPC because
1.) When you're churning and burning affiliate offers like zip submits and teeth whitening, the offers are gonna be dead as dogshit before you rank well enough to pull in any traffic. Blah blah you can build a site and change monetization... forget it. I go PPC, I have full control over my budget and I know exactly what my money is going to get me. Not leaving my bottom line to chance with forum speculations over algorithms where everyone is an expert cuz they read fuckin SEOMoz or some shit.
2.) If you want to do SEO make some real money and become a salesman for a brokerage house. If you're gonna spend your days shucking and jiving clients out of their money and then trying to explain overcomplicated bullshit to people who will never understand it, at least get paid. SEOs, largely, are snake oil salesmen. Sorry fellas. So if you have the type-A personality for that, sell cars or stocks.
3.) Paid Search will land you a job with security in the event that your own shit goes belly up. I've been doing it for like 7 or 8 years now and can walk onto any paid search gig outside of agency work. I'm working in-house now but before I came to this company I was charging my clients 15% of their monthly spend and wouldn't take any clients spending under $15k/mo. Do that math and figure out how many clients you'd need to live on a beach for the rest of your life. Exaggerating with that rest of your life shit of course, but you get the idea.
The world and the web are always going to be TEEMING with SEO "experts" because the metrics they use to boast success are very flexible.
I pitch a client or go on an interview or fire off a resume, I don't have to talk about keywords and positions and a bunch of shit that no savvy businessman cares about. I talk money, spent and made. New customers acquired as a direct result of MY WORK, not algorithmic blather. Year over year growth, not fuckin ranking reports.
Take proposals from 10 SEO firms and you'll be lucky to find one that promises link building (not article marketing, not press releases, not fucking meta tags, not bookmarking, not suggestions).
I was offered a position by one of the largest search agencies in the US to run their paid search efforts and they actually measure the value of their customer acquisitions based on the expected time it will take that person to pull their business. And it's a very short number of months.
I've got account reps at the major engines that fly to me when I need to see them and they're just as responsible for growing my account as I am. If something goes sideways in SEO, who is your backup? You're the fall guy, it's a mug's game.