In our case, I bought the PA, took an extra share of the gig money until it was paid off, and the PA is now owned by the band. The rule is if you leave the band, you forfeit your share of the PA. We're just starting into an upgrade bought and paid for on the same basis.
Regarding the lugging, setting up etc. one of the guitarists owns a van, he collects me and my gear plus the PA from my house. We all help lugging it into and out of the venue and whilst I do most of the setup, I prefer it this way as I'm a bit of a perfectionist and I like to know the gear isn't being abused.
Works for us, but then again we are all good friends both in and outside of the band, and there are no egos or prima donna's in the band.