The downside of course is that it's dead easy to clone these simple apps (like Twitter, TinyURL, etc.), which means the barrier to entry for your competition is quite low. This effect has been recently amplified with the boom in quality frameworks and dirt cheap infrastructure (EC2, App Engine).
The end result is that making a killer web app is not enough and you instead have to make sure you nail the social marketing of it and build up a large enough userbase that the brand/userbase becomes the real value.
Yes, it's easy to clone the features of these apps. So don't compete on features, compete on user experience.
37signals says "We hate email! Collaborate on the web!"
Tgethr says "We love email! Just archive it better!"
This is fantastic and I'll almost certainly be using it.
Oh, and I agree about Basecamp. I've only ever seen it used for message archive and the odd file sharing task.
One of my concerns though is that the email is not easy to give out. "No no it's together, but drop the o and the last e."
We'll see though, I'll give it a try.
Currently for this purpose of a public@somewhere.com (like our support@ type emails at Inkling), we use Tender (tenderapp.com) which does a great job already of managing a public discussion, support queues, etc.
But mainly we wanted something to do secure business collaboration (all traffic over SSL, and the ability to S/Mime encrypt all the email traffic for example). We also wanted reusable group email addresses "somewhere@tgethr.com", instead of looking up a crap load of email addresses or everyone being forced to create their own groups of email addresses in address books all over the place.
We also wanted a dead simple way to manage multiple of these groups and not feel forced to use a webapp to use the tool well. Didn't find the solution to all these wants out there, and we feel we have a knack - our opinion of course :) - of doing simple web apps for business, so we gave it a go of making something that works for us.
1. free
2. Combine the "basic", "plus" & "family" -- price it at $24
3. Combine "business basic" & "business pro" -- charge it at $99
Congrats on your launch!