The congeniality of all the members. I am not focused on any particular plant, but I always feel welcomed to any forum, even for just a quick 'help me' question. I also like how the organic v. chemical folks are able to have cordial discussions to better understand opposing views.
The responsiveness of Dave and Trish, as noted above by several others. So refreshing.
The accuracy and breadth of the database, and how it interconnects with My List. I have totally abandoned my previous system for tracking my plants and now use ATP exclusively for that. The added bonus is the ability to access all this information remotely.
The constant evolution of the site. I've only been a member for a few years and have been amazed at how much the site has changed (always for the better) in that short time. And virtually glitch-free!
The fun stuff - earning/giving/receiving acorns, raffles, photo contests.
The noticeable absence of a bunch of rules, and the self-regulating nature of the site. I've only seen a couple untoward remarks which the members quickly quashed and/or redirected in a cordial way.
The humor and kindness that permeates throughout the entire site, from members to moderators to administrators.
(I purposely did not number my responses, as they are all equally important.)
