I'v a 2008 1.6TDCI Fiesta, Getting 58ish MPG (Computer says 63)
Have done 5000 miles since December in mine and no issues. (Touch wood!)
Up to just over 103k now.
Very hard to get a 1.6TDCI here though, You can get the 1.4 handy though.
Highly recommended, Just buy a good one and keep on top of oil changes.
The Focus can be got with the 1.6TDCI, Same engine as mine but it has a DPF and different injectors.