Personally speaking, FLAC is a waste of time for general portable use (in terms of battery life and actual quality you'll get), jogging (ditto) and in-car use (quality vs ambient noise) but that will depend on how you feel about that. How you feel will obviously colour what you
think you hear
I'm starting to store in FLAC for home use, but am building a near-real-time transcoding rig to turn that into high-bitrate MP3 for portable use.
I've been using the Karma, iRiver, X5 and iPods portably with possibly the only phone (the Sony Qualia 010) on which I've been tell a high-bitrate compressed file without reference to the original recording. Yet I still stick to high-bitrate MP3's because of the convenience, more than acceptable quality for portable use and the ability to still retain a decent battery life.
The Karma is rather overrated here in terms of sound quality and the claims of it being the most audiophile MP3 player are somewhat optimistic, but it's a fine player
in the way it works. Possibly the best out there still in terms of stand-alone usage (playlisting on the player itself instead of on the PC, advanced mix features, etc). It's also ergonomically very sound. I like it.
The firmware and software (especially the software) still had some bugs to iron out, and obviously that is an issue with no further support being available. It's also not a USB Mass Storage device, so no plugging into a PC and expecting it to show up as a disc. And it is a bit of a brick compared to the X5, and in comparison with the new iPod... well, it's a bit like lining up a Sumo wrestler against Kate Moss.
Although it is a brick, I have to say that the shape is used very well and controls fall into the hand very well. Someone has really thought about how people use this. If it weren't for the various audio and functional/software bugs I might still have it. I dare say the less exacting could be happy even with those bugs.
Compared with the Karma (or the iPod), the iAudio X5 is a backward step in terms of a large-capacity music player, both in navigation and selection. But it does so much more... and if that's important will depends on whether you really use those additional features. It is however among the best of the purely USB Mass Storage players, which means all you do to add tunes is by drag & drop. This can be a pain though as your music collection increases, especially beyond the capacity of the player.
Again personally, for your use I'd say re-evaluate high-bitrate compressed files and widen your player horizons.