Nokia have publicly said that Nokia Software Updates to the N93, down since November 3rd, will remain suspended until 'early 2007'. This is due to technical issues with using NSU with the next-gen N93 processor, apparently. The new v20.0.058 firmware is now well established at all main Nokia service centres though*. 

* depending on product code/region, obviously...

Thanks to the several people who emailed in about this and also to Darla and the Howard Forums guys...