Roby on Rails for a large community?

That's like asking if a car goes fast enough to get you between two
cities in one hour.

Depends on the car, depends on the distance between cities, depends on
the driver.

Depends on the code and server, depends on the community requirements,
depends on the programmer.

I'm not trying to be flip with you. You've just asked as question
that's impossible for anyone on this list to answer.

Rails can be fast. Rails can be flexible. But it's not a magic
pill. You will run into performance problems and pain points, and
you'll have to work through them just like you would with any language
or framework. Rails is also alive and changing (very much so). So
"the performance" of Ruby on Rails is a constantly moving benchmark.

HTH,
Kevin Skoglund

Basically what I was going to say.

I also don't really think a few 1000 users constitutes a large
community, but that is relative. Twitter has something like 300,000
users and is built with Rails, maybe that answers part of your
question?