I've installed it by moving the .apk in data/app folder and setting permissions with rootexplorer. It works well on rooted Samsung galaxy s II (GT-I9100). Unfortunately I've found 2 minor problems (pheraps already noted) as today.
1) does not start when double-tapping the home button
2) crashes when selecting the "search the web/search on internet" option (the one that appears immediately after the "I'm sorry, I don't have the answer" message)
I'm not sure.. But if I'm not mistaken the possible solution to 1) may be changing current package name (com.vlingo.midas) into the one of the stock voice assistant (for galaxy s II -> com.vlingo.client.samsung) by editing the androidmanifest.xml in the .apk.
I'm not capable to do such task (even after reading several tutorials on this and other forums). Is it possible to verify this assumption?