Ok, so after months of doing things manually with SABNZB I installed Sonarr last night. Took about 10 minutes to set up (first time ever doing something like this, had a look at the sickbeard thread as well). I must say it is a real nice program to use. Add a series, you can choose to look for new episodes only or all missing ones, and it immediately grabs the nzb's. Added existing series from my series folder, and it picked up about 95% correctly (a few had different spelling, which you can immediately correct and then grab the correct series, like Mr Norrel instead of Mister Norrel).
The only issue I saw was that the first few NZB's it flagged as containing an archived file and then it just picked a different NZB. This does not happen often when I do things manually, so I was just surprised to see it. Nice that it kicks those NZB's out within the first minute of downloading (think SABNZB can also do this?).
The other cool thing with Sonarr is that it moves the completed downloads to your specified series folder (think you had to set up something in Sickbeard to do this?) and then Plex automatically picks up the new shows added. So now by just adding Sonarr the whole process is automated (like Sickbeard but it seems simpler than the SB setup guide for me).