I am on a number of different teams and love it. I also have 2 non-VA clients that I work with. Some VAs really enjoy being on a team and some use it as a stepping-stone to learning more. Communication between the team owner and the team member is key to figuring out which way the team member is wanting to go.
The team owners that I work with will not provide a service that they can't do because sometimes things happen and the team member can't do it. They realize that the team member is probably on more than one team plus they may have their own clients. As far as team members just disappearing, unfortunately, that does happen. That's when the team owner has to do their due diligence and chat with other multi-VA owners to see if they've had good or bad experiences with VAs.
As far as Melissa's comment, "Well, ask yourself what you would do if you were working for someone else rather than being your own boss. If you could make $35 an hour or more on your own, but only $15-$20 an hour (or even less) working for another VA, then what would you do if you had the chance?" - - - I am my own boss. I can and have told a multi-VA owner yes or no on certain projects. Also, most (not all) multi-VA owners know that if they are going to have a reliable team member, they can't pay $15-$20 an hour. They do need to make more than the team member because they're the ones that are out their marketing but most pay $25 per hour and up. It depends on the services the team member can provide and the rate the team owner is charging their client. If a team owner is charging $75 per hour, they don't have an issue with paying their team member(s) $30-$40 per hour, as long as they're doing a great job and are dependable.
Also, as a team member, multi-VA owners should still not provide benefits, etc. The team member is still a business owner and has to take care of those things themselves. If you want an 'employee', that's when you provide benefits, etc.
As a VA who is thinking about becoming a multi-VA business owner, think about your business and if you want the responsibility of having team members or if your business is just growing enough where you need to subcontract things out every once in a while. A team member is someone who has consistent work on your team. A subcontractor is someone who helps you with a project once in a while.
OK - I think that's about it for my two cents.