In my experience, the problem's often the opposite. With most startups, the accountant's job is to tell you when you're being woefully irresponsible with your cash and are about to fail because of it. That's harsh news to give to a friend.
The first company I worked at had an accountant that was a friend of all 3 founders. She was quite well qualified - Ph.D in accounting, taught at Bentley, had previously worked at several big companies. But she was not comfortable saying "No, we don't have the money for this" when the founders did something stupid, like hiring an expensive engineer sight-unseen from China or delaying the product launch by 6 months while the engineering team pursued a different direction.
We ended up going out of business rather abruptly when a $6M bridge loan from the VCs came due and there was no cash to pay it off. My boss (who was the only member of the management team who wasn't previously friends with the accountant) was incredulous that she could have forgotten that we needed $6M ASAP. Of course, she hadn't forgotten at all. She just wasn't comfortable telling management "Your dreams are about to go up in smoke unless we get more cash quickly and drastically cut expenses." Which is completely understandable in a friend, and completely unforgivable in an accountant.
I think what Bart means is that you should not let a friend or family member do it for free. There is no official business agreement then which makes it difficult to get things done. You can't complain if you are not paying for the service. It might also get personal.