- Not a huge fan of the "Pingdom killing" tagline in the title here. It sends a negative message that's unneeded, IMHO.
- I like the main page, but the multiple black boxes that popped up are distracting from the main content. Specifically, the "we're not here now" Contact button in the bottom-right, in addition to the Support button and the Sign Up button.
- You can't drag the scrollbar on the "Edit Check" page - it selects part of the page instead.
Other than those points, some small stuff: it doesn't say how I get notifications, the "contact us" black button obscures the "Follow Us" when you scroll to the bottom of the page, and, like bhauer mentions, the color depth seems a bit much - it's almost TO flashy.
All criticism aside: I'm still using it for my personal website :-) It looks like a good product, so keep up the good work!