Note: This guide was written during 2008 when Underfoot was the main expansion pack. It may be inaccurate for players currently on live. It contains a lot of information, some of which may still be useful to players which is why I have decided to preserve the guide. If you haven't already I recommend you read my Old Commonlands Leveling Guide.
The Obliteration mobs in Old Commonlands are a great source of experience to players whom are at least level 80 and above. Although 80 is very low to come here, someone with a ton of AAs at that level (over 2k) and very good gear will be able to handle these mobs in small groups, which is luckily the main way they come.
My favorite level to hunt here is around level 90. I grinded out about 750 AAs in this area and was getting about 16 - 20 an hour depending on what type of potion I was using. At the time I was doing this good here I was at level 90 with 2.3k AAs, I could handle about 8 of the mobs at a time without much of a problem.
There are multiple camps for these Obliteration mobs and depending on how many AAs you have and your level will determine how many you're able to clear. At my aforementioned level I was able to clear all of the Obliteration Camps within 30 minutes.
It took a little bit longer when I encountered too many named mobs; the named mobs have a chance to spawn at every camp throughout Old Commonlands. There are four camps that I normally traveled between while running my cycle in Old Commonlands. A map of these camps can be found just below.
Each of the Obliteration camps are marked on the map with blue. If I am not able to handle a huge amount of mobs and I can't even clear an entire camp because I am short on AAs or Levels I do the camp in the far northeast and/or the entrance camp that you cross when entering the zone. Both of these camps have a good amount of "two-packs" of mobs which are easy to solo. You still have to be careful and watchout for the large walking packs of four but once you learn their patrol patterns I wouldn't worry too much.
As you level up and can start to handle more and more at once you can move to the more southern camps. These camps have packs of mobs that will almost always come in 3 or 4s. Except for the simple blue line underneath the lake. This is a little destroyed village type thing than a camp and has quite a few of the Obliteration mobs in singles.