Has anyone organised a conference or a study-day on their own? I called for volunteers twice, but 4 weeks have passed and I have not received a single offer yet. Maybe my idea is doomed.

I have, and for a single day event perfectly possible by yourself (and some secretarial support from Uni) - means you get all the credit too.
I'd persevere if I were you. Let me know if you want any tips.

I've organised 2 conferences with one other postgrad student each time. To be honest though either of us could have done the work on our own. I think it's completely possible (depending on the scale of the conference). It just made it more sociable to work together on it. In some ways it was harder because we had to run everything passed the other person.

Good luck and likewise, I'm happy to help if you need any tips or advice

Thanks...
Well, I think that it's going to be a one day workshop or a study day instead of a conference...
Problem is that I live 3 hours away from campus... which means that I will have to make most arrangements via email...

I have just asked for volunteers (for the third time) and waiting...

Not many people from the department seem to be interested in it as it will be discussing a theory that is entirely pioneering and foreign in the field. Yet, the examiners of my thesis thought that it's definitely worth a study day, and encouraged me to organise it!

My conference was on a very niche topic, and as GrumpyMule says it makes it easier not having to run anything by anyone. I was free to organize it how I wanted, which I thoroughly enjoyed. I was also off-campus, but making arrangements by email easy enough. Having some admin support really handy though, but department will probably have someone to help.
Pitfalls I remember:
Not good enough signage for delegates to find the room.
Room too small in the end!
Water I ordered didn't arrive, should have had catering number at hand.

Hi Mara, please let us know how it goes! I'm quite keen on organising a study day, or something similar, and my department is absolutely tiny and studying very disparate topics so I doubt anyone would want to help me. Best of luck, N.