This looks really cool! A bit of design/copy feedback, none of it terribly urgent of course. Using Chrome 13 on OS X.

- Copy problem on the main challenges page: "Solve challenging programming questions and land -on- your dream job."

- On the challenges page "Solve This" buttons, the text is too high within the button, isn't centered.

- "Are you a great company for hackers?" box on the challenges page has weird stray space at the bottom of the box. Either vertically center the contents of the box or cut off the bottom.

- Typing error in the FAQ: "No worries, the remaining invites automatically get-s- added for the next month." Sort of awkward anyway, maybe "automatically roll over to the next month" is better?

- On my laptop, the live chat tab covers up the "All Rights Reserved" line, which doesn't matter but is a little visually annoying.

- The check marks and X's on the pricing page aren't aligned correctly with the row labels. They're aligned by the bottom of the text to the bottom of the icon, but the icons are bigger so it looks off. You should align the center of the text to the center of the icon.

- "Buy Now" buttons on the pricing page aren't centered correctly within the columns

- This is a small one, but maybe "Recruit" and "Challenges" don't match very well as the two halves of your site. They aren't the same part of speech and don't perfectly convey the two areas. Maybe something like "Get Hired" vs. "Recruit" would more clearly convey the split?

- The "About" page could do with being re-worked in a lot of ways. The spacing is pretty messed up (for example, YC branding has tons of space above, none below), and the paragraph format makes no sense for the information you're conveying. If you want to include companies you've worked for, why not make them a list. Overall, this page doesn't seem to serve any effective purpose beyond being a placeholder for some eventual page. There are also a ton of copy errors:

"At Interviewstreet[Isn't the 'S' capitalized in your brand?], we are looking to change the way the recruitment industry works. We are a team of five hardcore hackers and our Hall of Fame reads as[This is really unclear and awkward language. A Hall of Fame is usually comprised of people, not their accomplishments. If you want to keep it, change "reads as" to "includes," but it might be better to say something like "with experience at companies like"] MediaWiki, GNOME, Firefox, Libreoffice and Hadoop hackers, multiple Google Summer of Code participants, ex-Yahoo!, ex-Amazon and ex-IBM . Having worked in top Silicon Valley firms, we understand what hackers look for in their perfect job and[New sentence here?] with InterviewStreet, we hope to match programmers with the best jobs out there[Needs punctuation]"

and

"We are always online - just hit an e-mail["hit an e-mail" is a strange phrase; maybe it's lingo I don't know or something but I've never heard it. What's the advantage over "send?"] to team@interviewstreet.com (or) call us at 512-800-3815,[New sentence?] we will get back to you! save[Capitalize] the precious time of your employees[Maybe "Save your employees' precious time" is better, but I'm not sure what you even mean by this, or why it's here.] :-) Hiring is fun from now on!"

- "Contact Us" page is also a little weird. If I'm in "Challenges" and click on the link in the footer, it takes me to the "Recruit" tab for some reason. The spacing is strange: there's a ton of vertical space in between "Recruit" and "Contact Us," but the fields and field labels and submit button are all jammed together. My eye loses track of which field labels apply to which fields unless I start at the top and move down.