MACLOVER1.1  Simplifies my life a great deal.   
(Version 1.8.3)

GREG RAVEN  It's wonderful having a new version of MAMP Pro. I'd stopped using the old version because the developer seemed to have abandoned it, and between the built-in Apache server with Mac OS X and the new, easy-to-install MySQL, it was easier to roll my own local development server.

But now I'm back with MAMP Pro, not only for the ease of use, but for the little extras that are difficult to do when rolling your own. As opposed to using the built-in server, MAMP Pro also allows you to keep most of your development server files outside of the /etc/ folder, which makes them easier to work with, back up, keep track of, etc. -- especially through the OS upgrade process.

So far, I've come across only a couple of gotchas.

First, even though there seems to be an httpd.conf file in the conf folder inside the MAMP directory, it's not the one that controls the behavior of MAMP Pro. For that, you have to go into your /Library/Application Support/appsolute/MAMP PRO/conf folder. Because MAMP Pro puts all the NameVirtualHost and VirtualHost info inside the httpd.conf file, you'll have to take a step back from doing it the new Apache way, but it's not that big a deal. I have just over a dozen virtual hosts on my machine, and I set them up in what seemed to be a few minutes.

Second, MAMP Pro isn't really ready out of the box to run a local instance of Movable Type. WordPress is just about a no-brainer, but with MT, you can wander into blind alleys that seem to have no exit. I finally got mine to run by setting up my SQLite databases under the cgi-bin directory, rather than in the /db/sqlite section of MAMP Pro. Of course, even once you get it running, there are perl modules missing so MT throws error messages all over, but you can work through them ... at least to get your development instance working.

About the only thing on my wish list is that it would be nice to be able to store the MAMP and MAMP Pro files someplace other than the /Applications directory, because that's not the way I have may files arranged.

Bottom line: If you need a development server environment and don't feel like fighting with BitNami or xampp, or rolling your own, or making do with the lesser utility of a VirtualHostX-based system, MAMP Pro is just about the shortest way of getting there.  
(Version 1.8.2)

JASON EMANUELSON  Their contact form does not work (autoresponder with mail failure notice - address does not exist), and thus one is unable to ask questions of the developer. Something to be mindful of when purchasing software like this.  
(Version 1.8.1)

WRELEVEN  Actually a pretty cool package. It does use some odd directories to keep everything together and ensure that it doesn't disturb the apple/standard installed servers.

Though I was happy to see Snow Leopard support, I was disappointed that none of the MAMP software is 64bit. The pro version is quite welcome and truly makes it easy to manage the apache server.  
(Version 1.8)

KLAGRECA  MAMP Pro should include an FTP server and SSL support if wants to differentiate itself more from the "basic" version. I'd be glad to pay more for the PRO version if these services were included.  
(Version 1.7.2)

COCOANUT  I have not used this yet but the thought of a simple server environment setup for me to do development and testing is very appealing. I hope this works out, seems great!  
(Version 1.7.2)

ALJUK  Awesome. A brilliant development solution. Very flexible, virtual hosts, and the ability to serve up sites for clients to see and test straight from my laptop. Extremely impressed, straight 5 *****.  
(Version 1.7)

ERIC CALDWELL  I have been running MAMP for a while and editing config files, hosts files, etc. since I develop web sites locally. This inexpensive tool made that SO much easier. Another benefit is that MAMP Pro actually moves your DB's to /Libarary/xxx making upgarding the MAMP core files (Apache, PHP, etc.) a breeze!

If you put a value on your time, then this product is worth the money. MAMP Pro 1.1 and MAMP 1.5b1 work nicely together. The nice thing about MAMP 1.5b1 is that it now includes the Intel ZEND Optimizer which I had to code in the php.ini by hand before. No more...  
(Version 1.1)