Stick with a plugin for submissions or allow “contributors” to register?

I’ve been using the plugin TDO Mini Forms to allow readers to submit posts to some tech websites I run without having to register through the WordPress system. The plugin has a lot of quirks, and since I switched to WordPress MU, it has even more, and I think it’ll be tough to find a theme that is properly configured for what I need.

I am now considering just allowing readers to register with the sites as contributors so they can draft their own posts in the WordPress UI. This way I figure they can add legitimate profiles and themes should “just work” in terms of displaying the proper author attribution.

My question is: is there any danger to allowing people to register as contributors? I use extremely complicated and secure passwords for my admin and author accounts, so I’m not too worried about those (they’re randomly generated with 1Password). But I’m wondering about things like how many users WordPress (and WordPress MU) can competently handle, etc. I don’t expect hundreds of signups, but you never know.

Thanks for any advice.