Choreography is a mystery art. How it happens - or indeed what happens - is as elusive to define as pinning down a brainstorm. There is no solid stuff, no rules, no pre-formed maxims, everything moves; the choreographer goes into a studio, finds some dancers, finds some music, finds some moves, finds some light and atmosphere - and this agglomeration of variables goes out on stage all too often to fall flat, a soufflé that didn't rise. It was insufficiently skilled, or its ingredients were stale, or it lacked the leavening of a compelling imagination or the flavour of real emotional imperative. But what is going on?

A second coming for Michael Clark's recent Barbican commission Come, Been, Gone. Eight months after the London premiere (on which I opined unenthusiastically below last October), he has added another 20 minutes of choreography, they said, with new costumes and artworks. The revision is also now artfully retitled Come, Been and Gone. Not comma-Gone. And Gone. Makes all the difference.

A Balanchine on a mixed bill is a reminder of what a choreographer should desire to offer his audience: a specific new experience of art each time,  not a repeated thumbprint in every ballet. Balanchine grew up in a borderless theatre country - jazz, music hall, Broadway, Cubism, Russian imperialism, folklore, classical piano studies, all soaked his personality and fed his imagination.

In a shock that will deeply upset US and UK ballet, leading young British choreographer Christopher Wheeldon has abandoned his own company, Morphoses, which he set up in the US less than three years ago as a rare example of a choreographer-led ballet troupe. His former executive director has pledged to continue the company under a series of annual guest curators from different artistic disciplines.

Extraordinary lives dancers lead at Covent Garden - in a single day rushing between studios to rehearse the tortured, introspective Mayerling, the pristine classicism of The Sleeping Beauty, the off-centre acrobatics of Balanchine’s Agon and the static wriggles and hip-snaps of Wayne McGregor. All of these works are currently in Royal Ballet repertory, and you can see Ed Watson, Yuhui Choe, Johan Kobborg and an array of others on stage at the moment in all or any of these. But at what cost to communicating hugely different styles of choreography?

At its best (ie when it’s not trying to be gimmicky and snare so-called “new audiences”), Rambert is unique in Britain in providing music and dance as theatre. No other company matches it in commitment to this, not even the Royal Ballet, which long ago adopted cloth ears when it comes to new ballet music. Last night at Sadler’s Wells Rambert’s newest triple bill was a fine sample of this kind of evening, a delight to anyone with musical interests, and parading three unbeatable British choreographic talents.

Fleeting snippets of Vaslav Nijinsky apparently dancing on primitive film do, astonishingly, seem to capture his legendary liquidity of movement and capacity for making stillness arresting. But are they real?

Where to start with reviewing the "Diaghilev" evening of new choreographies at Sadler’s Wells last night? With the cool clean head of Wayne McGregor’s or the hot poxed genitals of Javier de Frutos’s? Well, as it’s a 100th birthday party for Diaghilev's iconoclastic Ballets Russes, there’s no harm in pointing out that the poxed genitals are an awful lot more amusing (with the accent on awful) than the familiar McGregorian chant of BSc theses to swot up while watching his dances.

Rubies is a ballet for a girl comfortable with her curves, who can slink her hips and tip her bottom and relish seeing the men’s eyes widen. That the said girl is a ballerina, for whom curves are usually anathema, shows the personality challenge that this snazzy, jazzy George Balanchine ballet sets to its leading lady.

Johan Persson took photographs of Kim Brandstrup's new ballet with Tamara Rojo, Goldberg, which was premiered at the Linbury Studio Theatre, Royal Opera House, on 21 September 2009. Music is J S Bach's Goldberg Variations, designs Richard Hudson, lighting Paule Constable, video Leo Warner for Fifty Nine Productions Ltd, sound Ian Dearden. Performed by Tamara Rojo, Tom Whitehead, Steven McRae, Clara Barbera, Laura Caldow, Tommy Franzén, Riccardo Meneghini. Pianists Philip Gammon and Henry Roche.