Just some quick observations. I like the general minimalistic monochrome theme. It's just the execution that lacks.
Logo - The simple wordmark is fine, but you should render it with a bolder font - That thin looking plus looks cheap. Also, the rendering should be antialiased - right now there are some really rough jagged edges in the logo text. Make sure it's evenly positioned (There's more padding under than over it as of now).
The font looks great, but you need a better fallback. You haven't linked the web fonts in properly, because some in places it renders as intended, but in other places it falls back to the browser default, which is a serif-font in most cases. It looks hideous in contrast to the very modern typeface.
The hero-block should have text positioned a bit further down (Same issue as with the logo). Also, consider bolding the first line to add contrast to the subheading.
The buttons in the hero bar have the fonts positioned wrong. This might be down to my system not picking up the same font as you have used. I would suggest to just use plain helvetica for buttons and main text and leave special fonts for headings.
The columns in the main section are too wide on my screen. I would suggest that you set the page in a fixed width grid - it's simpler to control the layout. Also, the gutter is way too big, to the point of having less margin on the sides than gutter between columns, which makes the layout look cut in half.
On the front page, you have two links between columns, that are centered. They look strange like they should have gone together with the left column, but have drifted too far to the right. At least put a horizontal ruler above, to separate from the columns above.
Hope that helps.
Edit: Just noticed. If you resize the page under a certain size, the menu jumps down below the logo, which is fine. But since the text is white and the background is an unrepeated image, it becomes white text on white background. Related - on the shorter pages (Such as contact), the footer ends before the screen does (on a large resolution anyway), which means that the white background comes after the dark red colour. Just set the same dark red colour as body background.
Here's[1] a screenshot from Chrome 24.0.1312.52 on Ubuntu 12.10. You can see jagged rendering on the logo and headline, the buttons look a little funny (padding? font?) and the top nav uses an inconsistent font.
I believe it is useful information for the owner of the web site. Whether you like it or not, people make decisions based on seemingly irrational factors, such as the design of the web site. It is particularly regrettable in this case, as the main design idea of the site is fine, but there are some glaring errors in the implementation. It would be simple enough to fix and could make a big difference for the company.
You need to take the bare minimum ten seconds or so to go into some actual detail in order for a comment like that to be useful. This is why you also have a reply from the creator prompting you for further detail. If you're really busy, at least give some impression of your screen size. If you have more time, maybe link to a screenshot. Vague criticism alone is worthless though.
Personally I'd say that the font weights are far too low on much of the text. Thin text is in vogue and often looks great, but it's a bit overdone in this example. The phrase "Address book storage you can trust" at the top practically bleeds into its own red background. The sentence below is less readable still. And the text in the two buttons below that isn't vertically centered at all.
