Hello James,
I have only been in the industry for about 4 years, but nearly every property manager I've come across is familiar with Yardi. I believe they are widely regarded as the go to management software (at least here in San Francisco). That being said, they take advantage of this, and charge a premium for the software.
We manage around 1,500 units in the San Francisco Bay Area, and one of our largest concerns with changing programs (currently using an older version of Yardi) is carrying the data over to a new program. That, and the learning curve involved with learning a completely new software. If you don't have many units, carrying data to a new program may not be such a big deal. Some companies also boast that they can carry information over, but it's not as simple as it sounds. So regarding the marriage metaphor, it's probably harder to cut the cord the longer you're with the company.
All three owners of our company have been in the industry for over 25 years. One of them is voting for Appfolio (he doesn't manage property), the other two are voting to stay with Yardi. I just signed up for a webinar on March 3rd to learn more about Yardi Genesis 2. But it looks like we are leaning toward staying with them.
Unfortunately, I don't have a lot of experience with the add-on related services.
I hope this helped a little bit. Here is the link to another thread that someone directed me to when I was asking a similar question. There are a few other threads about property management software on the forums. Another user directed me to this one:
www.multifamilyinsiders.com/apartment-id...-management-software
Check the dates on the posts, as a lot of these companies have made tweaks over the past few years.