SEO for months and months?

I see on SEO sites where they say they'll work to optimize your site for like 3 or 4 keyword phrases of your choice for up to 6 months. What does this mean? Why can't you just get the keywords/phrases you want, optimize the webpage, and be done with it in a matter of minutes or hours rather than having to optimize it on a daily basis? What's the need I mean I can understand working on backlinks but why would you need to spend time each day optimizing for a certain keyword/phrase what do they do?

Well,

I would say that they need to monitor how their editing of the site effect placemen.

They will need to build links like you said, but if they start to work on a PPC campaign, they will monitor that.

Also, a google dance happens on a couple time a year, meaning that they won't actually see any 'real' results until that happens, which could be 6 months, not to mention they might have to get your site out of the sandbox first, and that take a while too.

6 months for SEO work is a good estimate, expect more time for even better results.

In order to do proper SEO you need time, and lots of it. Optimizing a site or a pge for keywords can be done in 1-5 days, so it is not a big deal. But, as we all know, the bit deal with SEO is not the on-page optimization, but the off-page optimization. That means inbound links with the right anchor text.

Any good SEO will take 1-10 hours a day (depending on how devoted you are) to get going, with finding new link partners, approaching them, adding links, checking links, etc. This is what takes the time, and this is what costs the money.

From what I've seen, unless you are going to do this yourself, it is way out of most people's price range. If you're paying an SEO firm to do this, you might as well just emply someone to sit there full time and search, search search... the only ones that I've seen that are close to affordable are indian firms that hire people for $2 a day to do this for you. Sure, they get a few, but these are VERY rarely good quality, so are almost useless anyway.

In short, if you want it done, do it yourself. You'll know what's happening, where you're linking to, and who's linking to you. SEO is a very hard game, but when you can get it right 9and you did it yourself) it pays off very well.

The easy way is to learn a few basic SEO tips, like using the keyword in your title, a header, a link and a couple of times in the text. Don't worry about the exact number of times you are supposed to repeat a keyword according to some so called expert.

Use the simple rules above and write one article a day every day and add it to your site. You'll be swimming in traffic within a few months.

Have a look at SEO Chat, its quite a good resource for SEO related information.

Displeaser

I should be getting paid for the number of times i mention this book!
I would recommend getting hold of "SEO for Dummies" - only about £15 from amazon.
I've found it to be an essential resource, and although I'm not there yet with my site, it's already getting improved hits (getting 10x more hits since August!)

Even my Dad could understand it and he's a total Luddite.

I agree with most of what has been said already. Since you don't understand what the SEO experts? will be doing with all that time, it is clear you haven't yet learned a lot about the subject.
I am not criticizing, just observing. If you don't know what they do, how can you monitor them?
You are better off to do some study on SEO. Nobody is a true expert, because only so much is revealed by search engines. The rest comes through observation of what works for others.
Do some reading, and especially pay attention to how to form anchor text for links.
You'll be better off if you do the research and become your own SEO expert.