I'm provisionally giving Reframe It 5 stars. It's a great idea and I genuinely expect to love it.
I must add however, that though I agree to grant Reframe It unlimited and complete use of my comments in promotional screenshots, I retain the right to use my personal content anywhere I choose, and will do so freely at any time and in any venue of my choosing.
I have negotiated contracts before. Agreements like that represented in your proffer of a disclaimer--especially agreements specific to the Internet, or indeed, any agreement at all in real life--only try to civilize what is always, in fact, The Wild West. In the Wild West, parties put their guns on the table and agree to attempt to agree. It is in that spirit I have agreed to your off-putting assertion of all rights generally when you only need one specific right. I have agreed to that specific right, but my agreement stops there.
Should you wish not to accept my transfer of certain rights to you by my amendment to your License, you are free to cancel my Reframe It account instantly. Should you choose not to cancel, I will take it as tacit agreement to the condition I have set forth.
And, yes, guys, Creative Commons might work better for you.