First, the good. Josh and Amy's suggestions - Johnny Cash's 'Hurt' and Pet Shop Boys' 'Always On My Mind' - are perfect, as covers that come from a position of respect but that adopt a dramatically different approach to the original and in doing so offer a fascinating new perspective. As Amy notes, the latter is particularly remarkable for the way that it changes the resonance or subtext of the lyrics, as well as (of course) for finding a novel angle on a song previously performed by countless others. The Fall's improbable take on 'Lost In Music' and Soft Cell's 'Tainted Love' manage to pull off a similar feat. Sometimes this transformation or subversion occurs along the lines of gender, determined by who is singing the song: see the panel's suggestion, The Raincoats' cover of 'Lola', or (very recently) Soccer Mommy's 'I'm On Fire', which takes Bruce Springsteen's evocation of restless, irrepressible male desire and puts it in the mouth of a woman.
And then there's the bad, and the downright ugly. Josh and Rob single out David Bowie and Mick Jagger's duet 'Dancing In The Streets' as a career nadir for each of them; Amy criticises Madonna's version of 'American Pie' as a "horrendous misjudgement" that woefully misses the point; all three are rightly appalled by Catfish & The Bottlemen's car-crash mash-up of Kanye West's 'Black Skinhead' with the Black Keys' 'Howlin' For You' and Kasabian's 'Shoot The Runner'.
Beyond the assessments of quality lies the question of what prompts artists into recording or performing versions of other people's songs in the first place. On this point, I'd suggest, the panel are a little cynical. Most often, it's simply about a band setting out to pay tribute to their influences and thereby attempting to establish their place within a particular musical lineage. The Ramones and The Jesus & Mary Chain both sought to underline their affinities with The Beach Boys by covering 'Surfin' Safari' and 'Surfin' USA' respectively, while (for example) The Icarus Line honoured Spacemen 3 by producing a superior, amp-blowing version of 'Losing Touch With My Mind', Red Hot Chili Peppers attempted to prove their funk credentials with a cover of Stevie Wonder's 'Higher Ground' and The Flaming Lips couldn't pick a single Dark Side Of The Moon track so instead just covered the whole album.
However, covers are also regularly (to use Amy's neat phrase) a translation from one genre or generation to another: Jimi Hendrix taking Bob Dylan's 'All Along The Watchtower' from folk into rock, for instance. In some instances, it does seem to be a way of reaching new markets, whether deliberately or inadvertently. When Billy Bragg covered 'She's Leaving Home' for the NME's 1988 charity album Sgt Pepper Knew My Father, the formerly on-the-margins polemicist folkie suddenly found himself at the top of the UK singles charts - though, admittedly, that was largely because his effort was a joint double-A side with Wet Wet Wet. 'With A Little Help From My Friends' indeed.
Prospective starlets on American Idol and X Factor are compelled to perform familiar songs because it makes assessing them easier (there's already an established benchmark), and covers are certainly used by up-and-coming acts as a means of grabbing attention and padding out short live sets. Anyone who gets sniffy about covers should remember, too, that some of the most celebrated artists around rose to fame on the back of interpretations of songs that they had no hand in writing (Elvis being a prime example) or by extensively borrowing (stealing?) from others (hello there, Led Zep!), and that jazz has a long-established tradition of common standards that are reworked and rephrased by successive generations of musicians.
However, it's only fair that bands should confess to their borrowing: I recall a friend being (rightly) irritated by Fear Of Men for their failure to acknowledge at a gig that 'Pink Frost' was actually by The Chills, which made it seem as though they were trying to pass it off as their own. As Amy notes, it's also true that some artists' attempts at musical translation could be seen as troubling instances of cultural appropriation - most often, white musicians repackaging black music to make it palatable to a white audience.
Amy is spot on in decrying "earnest white-boy indie covers of pop songs" as a particularly egregious trend, one for which Radio 1's Live Lounge is chiefly responsible. Travis' take on Britney's 'Baby One More Time' may have set the tone, but the smirking xylophone-heavy Elbow cover of 'Independent Woman' (as cited by Amy) and the aforementioned Frankenstein's monster of a track created by Catfish & The Bottlemen are arguably the absolute nadir. (You'd hope that as a Radio 6 DJ Guy Garvey is now suitably embarrassed.) There are precious few instances of roles being reversed (i.e. pop artists covering indie songs), though Amy Winehouse's 'Valerie' is a notable exception.
Another very odd trend - one not discussed by the panel but identified by Spin - was the penchant of late 90s/early 00s (nu-)metal acts for covering classic songs of the 80s. Josh did raise the horrific spectre of Limp Bizkit's cover of George Michael's 'Faith', but could also have pointed to: Alien Ant Farm, who enjoyed their brief 15 minutes with a version of 'Smooth Criminal' transplanted to the white suburbs (see the video); Fear Factory, who roped Gary Numan into a cover of 'Cars'; Disturbed, whose surprisingly passable take on 'The Sound Of Silence' was preceded by covers of Genesis ('Land Of Confusion') and Tears For Fears ('Shout'); Coal Chamber, who contrived to get Ozzy Osbourne to contribute to a reworking of a Peter Gabriel track, 'Shock The Monkey'; Marilyn Manson, whose sinister 'Sweet Dreams (Are Made Of This)' was as good as his 'Tainted Love' was appalling; or Deftones, who at least showed off the best taste by choosing to cover The Cure, Cocteau Twins and Depeche Mode.
Finally, it's worth observing that cover versions can break careers as well as make them. Stephen Jones aka Babybird could only look on in horror as 'You're Gorgeous', a track about seedy glamour photographers and their subjects, was misunderstood and performed as a straightforward love song at countless open mic nights and weddings, before suffering perhaps the greatest indignity: a cover by The Wurzels. No matter how much material he's produced since, he can't seem to escape the shadow cast by that song and the thousands of mawkish versions it spawned.