Youpeee !!!
Froyo is finally here, sooner than I expected it !Thanks, Google !!!

Now, like every other geek with their new toy in hand, I tried most of the new things...
And all is great, but...
The install on SDCard is always greyed...

Then, I just read a tweet from Romain Guy explaining it in a few words.
Your application should add this line in the manifest

 xmlns:android="http://schemas.android.com/apk/res/android"
    android:installLocation="auto"
    ... >

in order to be installed by the end user on the SD Card.

http://developer.android.com/intl/fr/guide/appendix/install-location.html