A personal favorite good answer:

"I just started my twitter clone yesterday. I built a prototype in rails last night after chugging red bull! Each tweet is just database row with a giant many-to-many relationship. We're at 30 users already! I told my mom about it and she got a bunch of her coworkers to sign up.

We should probably cache or precompute some feeds, but we're fine for another 2,000 users."