I emailed my list of woes to Humax on Saturday 2nd, who to their credit replied later that evening which I wasn't expecting (particularly given some reports on here). They said they had been receiving "mixed reports" which they would pass to the development team for future updates, and couldn't promise to fix everything but would look into it.
They did however say the sluggishness, channel changing issue and crashing definitely shouldn't be happening and suggested a factory default reset. Luckily this doesn't actually wipe the recordings on the box so I had a go and I'm happy to say the crashing during standby is no longer happening and the on-screen programme listing keeps up when you changing channels. It's a bit quicker - still much slower than I'd like, but slightly better. This probably explains why some people are reporting no issues at all with the unit and others are tearing their hair out. It still has a useless interface and multiple things that could be better, but it's not crashing on me which was making it an expensive paperweight...
One thing I did notice last night is that the EPG on BBC2 (both SD and HD) took forever to display the Bowie tribute after Newsnight (even when I sat on the correct muxes), when the YouView EPG on my Sony TV and the old T2 box in the spare room both were updated hours earlier. I think FVP finally removed the snooker highlights about an hour before it went out. Not sure if this is FVP or Humax, but either way not good.
Finally does anyone know what the play signs surrounded by a dotted line are on the EPG? I thought it was "watch live" initially but it seems to show up on programmes up to an hour ahead.