This debate is largely irrelevant to most people who don't have high end gear (particularly headphones which can be disturbingly revealing). It really comes down to your specific situation and equipment. I have run endless double blind tests with lossless files and LAME encoded MP3s (at -V2 and -V0 VBR quality) and I can safely say that I can't tell the difference between those formats. 128Kbps AAC and MP3s are a different story. I could hear discernible differences with those bitrates against the lossless versions. With Amazon and iTunes now offering DRM-free 256Kbps files, I find the issue nearly moot.
I say "nearly moot" because I refuse to regularly pay out a minimum of $10 for digital albums that don't have the overhead of printing liner notes and pressing CDs. But I have purchased several Amazon $5 albums and even an iTunes album that was $7 that included a high resolution PDF of the liner notes.
As a result, I still buy most of my music on CD and vinyl and archive the files to Apple Lossless and rip those to LAME -V0 VBR MP3s for actual listening. Why keep a copy of large lossless files if MP3s are good enough? Chalk that up to my fear that one day I may want to transcode those lossless files to a new format that improves compression and maintains transparency or storage prices for DAPs and media become so cheap that I might as well just use the lossless versions as my primary playback files.