Your primary message: "PowerGrabber is an invitation manager. It captures the addresses from your inbound and outbound emails, so you can invite the people you email to join your LinkedIn™ network."
I don't know what an invitation manager is, captures sounds non-friendly. How about: PowerGrabber ensures the people you email are connected to you via LinkedIn. No more lost connections.
I'd also drop all the trademark symbols, whilst probably more legal it looks very corporate and almost scammy as it breaks the line flow.
I'd put the benefits above the "What is PowerGrabber" (you duplicate your appropriate primary marketing message, only with more detail)
In reality your benefits are that the people you email are your linkedin contacts. I'd spell this out by a short scenario about losing a contact that would be really valuable in the future. The benefits you list are complex and scary and marketing speak. "Systematically".
From the application point of view - the most useful data is who do I email the most that I'm not connected to? do you offer that? A video would help. The "how it works" image isn't clear as to how it works. Your best bet is to make a few screens in PowerPoint and record them as a video.
Your privacy policy is a pdf, i'd put that as html.
I'd also consider changing the logo as when I see that logo I think of the soviet union which is uhm, probably not appropriate :)
It's a neat idea and I'd use it if it worked with GMail and Mac. It solves a problem and is of clear value to the user, I'd make sure your marketing messages were similarly clear.
Just my $0.02