Check out this sample from Diablo in Finland.
I have asked them about their gear and recordings and they used a Line 6 POD for all of their albums despite the fact that they play through Mesa Boogie Triaxis Preamps and Mesa Power Amps with Lexicon Effects live.
I believe Meshuggah also used Line 6 for alot of their recent recordings.
I personally use it for recordings direct.
And like any Line 6 Pod 2.0, Pod Pro, etc, you need to know how to use them.
Don't record anything Direct without a cabinet Emulator turned on because it sounds over processed without it.
Don't use a cabinet emulator while plugged in to an amp and guitar cabinet because it while sound .
Hold the tap tempo buttons and turn the knobs to get more features activated.
You can add Presense or a Distortion boost by using that feature.
For Metal, you will probably only use the Rectifier Settings, Line 6 Insane or maybe the Modern for some lead and lower gain rythm guitar.
I personally never cared for POD Xt, XT Live or Veta because some of these extra controls either dissappeared or weren't worth the time figuring out.
IMO Pod Pro is cheap, simple and versatile.