I'm not a very cynical person so I've found the assemblies in my area (DC) to be a totally inspiring thing; I think they're absolutely worth participating in, supporting, and defending. That's not to say that the general trajectory of the Occupy* movement or of DC's occupation in particular is that promising.
The way they're run encourages broad participation, and they usually attract a few hundred people.
Decisions do actually get made, by consensus, without ever even resorting to modified consensus.
The process is explained thoroughly at the beginning, so that newcomers will understand what's going on and why it's important that we do it this way.
The clear process usually does prevent totally irrelevant interruptions from slowing down the meeting a lot.
People have consistently shot down the idea of presenting any statement of goals or demands for the movement; same with a proposal to express gratitude to the police, or to have marshalls at our marches.
The occupation has a set of guidelines, some vague, some fine, some objectionable. One of these is simply "obey the law." I think that got passed when only a handful of people were around and I think it will be very hard to replace it with something more sensible. If even one or two of us (anarchists, that is) had been present at the beginning we could have blocked it. That said, people have been ignoring that guideline without anyone stopping them or reporting them to the police.
The meetings drag on quite a bit for a variety of reasons. In my mind this would be okay except that it means committee meetings (which start afterward) happen pretty late.
On a related note, most committees meet at the same time, so it's hard to be on more than a handful of committees.
As far as I know, our assemblies don't publicize minutes or major decisions so if you miss one you have to do a fair amount of asking around in order to find out what happened. I imagine this would be tough to do if you didn't know anyone.
There's a particular style of speaking that seems to be expected at the GAs where certain things are always kept very vague (people's names, political affiliations/commitments, for example) which can be confusing or misleading. Also, there's a bad tendency of using vague all-inclusive "we" statements.
My favorite thing, though, about the occupation is milling around, chatting and eating, honestly.