There are quite a lot of inexpensive property management apps that can make your life and bookkeeping a lot easier.

QB is for bookkeeping.

As well as having it set up correctly [which may be more time / cost effective then attempting the setup on your own].If  you  use a bookkeeper, realize that they consider the work that they have done on your books as their property and not yours.

There is the pain of physically collecting but also it takes more effort for the bookkeeping than direct deposit. 

You will also incur annual higher book keeping costs.

The next one we might outsource is book keeping.

In your example the S&P investor invests zero time (save for a few seconds of mouse clicks), whereas the RE investor must invest significant time managing his properties (or managing the PM), facilitating financing, bookkeeping/accounting, etc.  

But there are a number of tasks that fall outside of systems, like bookkeeping, paying non-reoccurring bills, handling maintenance calls, etc.

I've known lots of investors who owned lots of stuff, but weren't able to dig their nails in and hang on and lost it all.So, maybe a good retort to these inquisitive minds might be "The number of properties one owns isn't as important as the cash flow one receives, but talking about one's income isn't polite so I only discuss it with my wife/husband/cpa/bookkeeper/cat/dog."

Communication problems, bookkeeping problems, tenant issues and the dreaded repair cost issues and misunderstandings.