You've got a nice clean site. (I'm a sucker for white space.)
Although you've had it since 2006, your domain name "danielmcmullan" is virtually useless in terms of web search for your targeted keyphrase "freelance web design". Consider purchasing a few additional ".com" domains containing targeted keyphrases and have your site resolve to the best one.
According to Yahoo! and Altavista, you've only got 16 IBL's, none in Google and your PageRank is nonexistent. Right now would be the best time to make the change in your domain name. You need to work hard toward acquiring relevant inbound links from related sites and directories.
In terms of on-page
SEO, you've done fairly well. Alt tags on images and plenty of keyword rich content but consider adding more link text within the content. Search engines eat this up. Make it work for you.
For example, these are "naturals" for link text:
"Web Design and Re-Design - Flash Sites and Animation - Banner Ads - Multimedia Presentations - Logos - User interface design and usability - Web application strategy and development."
I like the "two sentence" writing style. Short, descriptive and to the point. Perfect for the web.
You've wasted a lot of vertical space with the header graphics. Reduce the height of the header and move more content above the fold.
I don't care for the pixelated browser logos. You can clean them up at the same time you reduce the size of the header images.
Reduce vertical scrolling in the web portfolio page. Break the content into sections which link to additional pages.
I'd be concerned about duplicate content in the portfolio pages after clicking the "More Info>" links because you're repeating the left column content in each portfolio page. From a readability perspective, having the portfolio content restricted vertically to the right column makes it difficult to read from left to right without scrolling vertically. (Users hate that.)
Consider removing the duplicate content from the columns on the left and allow the web portfolio page content to span across the width of the page.
From a navigation perspective, having to scroll down the page to locate the next portfolio link is frustrating. You may wish to add some sort of "Next" and "Previous" navigation at the top of each portfolio page. Something similar to the web/print portfolio buttons on the home page would do nicely.
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