So here's the deal. I work a 9-5 as an in-house SEO/internet marketing guy. I am the only one on my team (currently) who "gets" SEO/IM.
To answer your question about salary, it really depends on the company and where you live. Obviously, if you live in a major metro, the salary is going to be a lot different than if you live in some small town. I strongly recommend looking at
http://www.glassdoor.com to find out what the average salary is for similar positions in your area. If you are just starting out in the corporate world, they will try to low ball you. If you can make it look on your resume that you have years of experience, obviously you will demand a higher salary.
The benefits of the corporate gig are:
1) Guaranteed salary and benefits. This is huge for me, my job has amazing benefits (insurance and 401k). I have a nice chunk of retirement money saved up and I'm still relatively young. The guaranteed check every 2 weeks is also nice. I know what I'm going to make.
2) Potential for career growth. SEO is great and all, but there is so much more potential for learning marketing. I've learned a lot in regards to media buying (both online and offline), direct response, print, etc. I am a much more well-rounded marketer than when I started.
3) Don't have to hustle (at least not as hard as affiliate/freelancing). You pretty much work at your own pace. Granted, you can get bosses who are assholes, but for the most part, I fuck around on the web for the better part of the week, and even do some client work/work on my own sites while at work.
4) Work on some cool shit. I am transitioning my career to an ad agency which has some major clients. Clients I never would be able to land while freelancing. These guys are designing amazing sites, mobile apps, etc for huge brands. It is pretty amazing to work on such a large project with a team that knows their shit. And to be able to tell your friends/people you meet 'Yeah, I made that shit'
5) Building a resume. You might start out small, but you will work your way up over time.
Now for the cons.
1) You will work with assholes. Obviously they won't come out and say it in the interview, but every work environment will have a couple of people that you won't get along with. They either won't understand SEO and will try to tell you what to do, they will be generally incompetent, or they might just be a flat out shithead. This is probably the worst part about working a corporate gig. You can't really control who you work with. The best advice I can give is talk to as many people who work there as possible to try and get a feel for the corporate culture.
2) Lack of freedom. This really depends where you work. Have a great idea for one of the company sites? Great! Now you just have to run it past your boss, and he runs it past his boss, who may or may not understand WTF is going on. You may have the freedom to do whatever the fuck you want, when in other cases you have to go through a process of approvals, of which one of those people higher up is likely to steal your idea and take credit for it at some point. Again, get an idea of the corporate culture and how much freedom your job would allow during interviews.
3) You spend a good amount of your life inside a fucking office. This sucks. Nice day out? Too fucking bad. You're stuck in your cubicle. Commuting can also suck depending on how far away you are from work and traffic.
Anyway, there's probably a lot more that I missed. But I hope I could clear some things up for you. If you do decide to go the corporate route, just make sure that the company is a good fit for you, personality wise and skill wise.
