I'm by default lazy and tend to misspell words on a regular basis. Not that I don't know how to spell - my fingers just tend to type them in the wrong order. I also like to have similar if not same dev environments on all my computers. This is where MAMP comes in.

However I never use the stock MAMP config - I tend to tinker with PHP and MySQL and Apache settings. This however can be a tricky business when it's time to upgrade to a new MAMP version.
For future reference here are the steps to follow:
1. Quit MAMP and rename the folder in Applications to something else
2. Download MAMP and install it into Applications folder
3. (Optional - if you're curious like me use DiffMerge to see what exactly changed between versions)
4. If you keep your sites in MAMP/htdocs folder copy MAMP-old/htdocs to MAMP/htdocs
5. To restore the database copy MAMP-old/db to MAMP/db
6. To restore MySQL settings copy MAMP-old/Library/my.conf to MAMP/Library/my.conf. If you have no such file you haven't made any customizations.
7. To restore Apache configuration merge your custom bits from MAMP-old/conf/apache/httpd.conf into MAMP/conf/apache/httpd.conf
8. To restore PHP configuration merge MAMP-old/conf/php5.3/php.ini into MAMP/conf/php5.3/php.ini and MAMP-old/conf/php5.2/php.ini into MAMP/conf/php5.2/php.ini
9. Remove MAMP-old from Applications
10. Restart MAMP