<p>I'm using Emma in my ant build to perform coverage reporting.  For those that have used Emma, is there a way to get the build to fail if the line coverage (or any type of coverage stat) does not meet a particular threshold?  e.g. if the line coverage is not 100%</p>

Not out of the box.
However, the
```
report.metrics
```
property or attribute of
```
<report></report>
```
can be set for
```
name, class, method, block
```
, and
```
line
```
.  See
Coverage Metrics
in the Emma reference.
Use a plain-text report then a regexp filter to set up a fail condition.