[sheepmullet]

Most of the problems are organisational rather than with estimating per se.

If I'm doing prod support for three different products and build work for two products, then I'm naturally going to be juggling priorities. There are a lot of different and changing variables in the mix and it makes committing to deadlines very difficult.

If an organisation wants to isolate developers and have them work on only build work for a single product estimation becomes much more accurate. Of course most orgs would rather less accurate estimation instead.