Interesting point. Yes, it would overwrite. But as we parse collectd packets, there shouldn't be any tags in the event at this point. When we call `decorate_event`, the rest of the tags are added:
```
input {                                                                          
  collectd {                                                                     
    port => 25827                                                                
    tags => ["whatever"]                                                         
  }                                                                              
}                                                                                
output {                                                                         
  stdout {                                                                       
    codec => "json"                                                              
  }                                                                              
}
```

Produces:
```
{"@version":"1","@timestamp":"2014-01-31T14:33:02.998Z","host":"kumina:production:lieters-klaptop.prot.plexis.eu","plugin":"memcached","collectd_type":"ps_count","tags":["_collectdNaN","whatever"],"processes":0,"threads":4.0}
```

But I'll create an ```add_tag``` function so more tags can be added.