Nice logo.
Get rid of the b&w stock image on the homepage.
Keep wording consistent: change "Complete our simple registration" to "Complete our simple sign-up form". On the registration page, change the "register" button to "Sign Up!"
Keep your logo in the top left corner of all your pages. It's nice that it gets out of the user's way after moving off of the homepage, but it's confusing.
Use a feedback form like the one on slacker.com (i.e. omnipresent) -- you'll be much more likely to get good feedback that way.
I really like the homepage design, but the content in the center of the page should be simpler and draw in users' attention (e.g. http://pixtures.s3.amazonaws.com/misc/mingle-process.jpg). You can offer a detailed explanation of your service after the user signs up -- or on the "see how it works" page... Or even just a little lower on the homepage.
Your homepage actually convinced me to sign up, but the "On your way to the MingleWeek" page is just plain daunting. So much text. No images. No simple instructions. Too much work before I'm able to see a reward. After I confirm my email address I should be taken to a page titled "Upload Your Photo" (i.e. no "Create Some Portraits") and there should be a big "upload" button in the center of my field of vision. While the homepage is really inviting, the pages after sign-up are less than inspiring.
The "Make a First Impression" page is cool. Make it easier to submit content. Don't even bother having multiple fields under the "Music" tab (i.e. Song, Musician, Album). Keep it simple: "Song Name" is enough. People will write "Song Name - Artist Name" in a single text field if they're so inclined. I would also suggest making all of the tabs omnipresent (e.g. http://pixtures.s3.amazonaws.com/misc/getting-to-know-you.jp...).
"Terms and Conditions, coming soon!" heh :)
P.S. Try to find a way to encourage a friendly atmosphere and community. That's why people visit social websites: the community. I would invite some of my friends to your service if there was a more compelling reason than "As the FlowMingle community grows, so do the number of people you can choose from." It seems like what you're trying to do is make a site geared more towards friends casually hanging out, having fun, and getting to know each other -- and I think that's great. Formal dating is overrated.
Cool concept. Good luck.
