I can't answer your call for native speakers' opinions, but I'll give
my $0.02.
I use it on Windows at work, and I like the suggestions and the
ability to quickly input proper nouns (especially media-related items,
like game titles).
I also installed it on my Mac at home, but I find it very inconvenient
because it doesn't support switching modes with the caps lock key (my
Mac has a US English keyboard with no dedicated 変換-related keys;
Kotoeri allows me to switch between 半角英数 and ひらがな with the caps lock
key).
Incidentally the Google Chinese IME (for Windows only, unfortunately)
is quite good.
-Aaron Madlon-Kay
On 12月10日, 午後2:01, Jean-Christophe Helary