I would add to that that even with an open air mic there are always situations when a remote is going to be easier than voice commands.
If you're OK with the idea of an always on Logitech Harmony then maybe you could consider an Android on a docking station or something like that. VoxWav Pro has an always on mode. At least it's a good, cheap way to test things out if you already have an Android.
http://voxcommando.com/mediawiki/index.php?title=VoxWavIn terms of HTPC control, voice control is especially excellent for asking for specific things -- playlists, songs/artists/albums by title, queuing a specific set of songs by title ("Queue playlist favourites, add artist Joan Armatrading, mix in some jazz tracks, add song All Along the Watchtower"), asking for a particular movie to play, specific episodes or seasons of a series, setting volume to a specific setting, etc. Once you've been doing this for years, it is hard to imagine going back to "old school" navigation with just a remote. But I still regularly pick up the remote to pause the movie by hand.
This is true whether one is using an Amulet or an always on solution. However the Amulet (or VoxWav) are generally more reliable ways to issue voice commands, with fewer issues than most open-mic solutions that most people are trying to use.