I have somewhat different thoughts on this issue. In my opinion, the Internet is and should be a heterogeneous environment. I am a relatively new member of Newgrounds.Com even though I have contributed only reviews recently. I have enjoyed Newgrounds and the excellent artists who contribute their work. However, for a good while I was unable to access Newgroundds AT ALL. This was simply due to the lame Internet connection I've had since only a few weeks ago. It was dialup and considerably slower than even 56k. Not only did the site take long to load: I couldn't even view movies or games.
If there was an alternative portal that could have been loaded even on my original connection or if this site, original and great as it is, got shut down, would I consider to use it? Of course, so I could have the opportunity to continue viewing other's work and possibley submit my own.
I do not think the portal concept should be patented or the site's source code even copyrighted. I simply think that there should always be alternatives to the mainstream. Yes, Newgrounds is the original: that can't change. However, there could be opportunities to extend Newgrounds's portal idea further and provide alternative pathways to share your artwork with others. Heterogeneity is good: provide competing Flash portals so the artists who call prefer their own "home" portal can have friendly competitions with other artists to improve their work! Have Flash portals compete with one another and strive to make their work constantly better (not that Newgrounds, of course, doesn't do that already =)). I disagree with ripping off people's work, especially for making a profit; but sites like Flipsided seem to merely need to start somewhere, even if it means borrowing others' ideas for a time.
Sites, like Newgrounds, evolve. Give Flipsided some time, and Flash artists may have another community where they can compete and make acquaintance with other artists other than those they are familiar with here! What we may see isn't mere copycatting but the possible start of an even larger Flash community overall.