There seems to be an issue on 1.0.6 that didn't exist on 1.0.0 when using a number of trackables of around 50+.
On 1.0.0 it does get some false positives sometimes when pointing at a random scene in the real world, but handles the number of trackables fine.
On 1.0.6 it freezes the camera view. Sometimes immediately after the app has started, sometimes about 20-30 seconds in. (Then the app hangs and asks to force close, see: http://pastebin.com/kYQunjCN)
1.0.0 ImageTargets sample with sample 2 trackables works fine. Replace with new data files with 50+ trackables, works fine.
1.0.6 ImageTargets sample with sample 2 trackables works fine. Replace with new data files with 50+ trackables, hangs after a few seconds.
Tested it on 2.1, 2.2 and 2.3.3 - HTC Desire, Samsung S2, Galaxy Tab, Galaxy Ace all having the same result.
Tested same data file works fine on iOS 3GS, iPad2, iPod, iPhone4 and 4S.