Community oriented Site - Flash or Not?

Hello people,

I’m about to start a pretty big project. I’m still in the planning phase right now. I’d like to hear your opinion. I want to make a site that will be community oriented. It will have all the basic stuff like: share photos and videos, about you… etc.
My designer wants to use flash for this project. I love flash and I’m pretty sure I could create the site with it. However, I don’t know whether I should stick with AJAX and use flash here and there, instead of making everything in Flash. One clear advantage i see is that I won’t have to deal with the way the site is displayed across different browsers and OS. My biggest concern is the management/maintenance part of the site. Would it be more work with flash?
What about security?

I’d like to hear what you guys have to say.