I just tested this on one of my apps (yakkstr.com) and 'rails c' and 'rails s' both startup in about 5 seconds. I'm on 1.8.7 and rails 3, not sure if that makes a difference, but 20-30 seconds doesn't mesh with my experience at all.
For me on 1.8.7, it takes about 7-8 seconds. Annoying because the application is empty, it's just 28 gems being loaded. On 1.9.2, it's 20 seconds or so.
I'm on a 2.66 GHZ i5 imac, not an SSD.