If you’re interested in search marketing, I would thoroughly recommend the weekly “Whiteboard Friday” videos on Moz, a site which most SEO specialists rate very highly. Last week they tackled “Why the Links You’ve Built Aren’t Helping Your Page Rank Higher“, which gave a good insight into some of the difficulties surrounding search engine optimisation.
I won’t go over what’s said in the presentation (although I’d recommend watching it), but there are two things we should take away. The first is that although we want links to our sites and our content, there’s no point in having just any old links. The ones which make a difference are from good sites, which are related to what we do, and are clearly linking to us as a reference for something they’re discussing. A link to your home page from a poorly-rated directory isn’t going to do you any good at all, especially if Google believes that there’s a commercial element to the link.
The second thing to realise is that building good links is really hard to do, and the opportunities are really limited. Throwing a couple of hundred quid each month at someone to “do SEO” isn’t going to get you an effective external link profile. That’s something you’ll need to work on yourself, using your knowledge of your industry, its media and your contacts.