Personally, one thing I've found that helps with estimates is to think in terms of days instead of hours, and to assume a fairly low productive amount of hours (5) within each day when converting back. (Yeah, you'd hope to be productive for more than 5 hours in a given work day, but there are a lot of little things that steal your focus and eat a lot of time away from your project without you realizing it. Fail to account for them at your peril).
The original estimate someone put forth for twitterific was 160 hours of development. Ask yourself, could you reasonably expect to sit down today and from scratch, have written something as polished as twitterific, in only 32 days? Knowing full well you will need to spend days banging your head against some problem that should have taken you 10 minutes but somehow cost you 6 hours, testing and fixing bugs, profiling and optimizing slow code paths, polishing interactions, tweaking animations, and going back to the drawing board when some piece of functionality doesn't quite feel right?
The testing and tweaking alone can last for weeks in high quality projects, and 32 days only gives you 4.5 weeks from start to finish. It's absurdly low.
The original estimate someone put forth for twitterific was 160 hours of development. Ask yourself, could you reasonably expect to sit down today and from scratch, have written something as polished as twitterific, in only 32 days? Knowing full well you will need to spend days banging your head against some problem that should have taken you 10 minutes but somehow cost you 6 hours, testing and fixing bugs, profiling and optimizing slow code paths, polishing interactions, tweaking animations, and going back to the drawing board when some piece of functionality doesn't quite feel right?
The testing and tweaking alone can last for weeks in high quality projects, and 32 days only gives you 4.5 weeks from start to finish. It's absurdly low.