You know the situation, lots of time pressure on the project, the client needs a little [treeview] [search optimizer] [birthday calendar] [pdf / cad / xxx viewer] [etc] (select or choose your own) addition to the SharePoint implementation.
There is no budget, because .. why should we by this ??! Doesn't it come with SharePoint ? We'll think about it when we see it working...
And you know you should use the dev / test environment to run these trials on .. but hey... sometimes there is only 1 environment...
STOP... Don't DO IT !!
Chances are that the 3rd party tool you are installing is NEVER going to leave the farm / web app / site collection, or you going to spend ALLOT of time cleaning up after you try to remove it.
Maybe you don't care what's left behind.. until you see the warnings appear in the health-analyzer.. Maybe you don't look in the health analyzer ? You will... once you install a CU or want to upgrade to SharePoint 2013.. Which won't work.. because there are some missing components ! ALERT ALERT ALERT !!! Of course you did a trial upgrade .. right !?!
The above scenarios I consider "lucky'", in one occasion I saw the whole farm die when I uninstalled a 3rd party product; giving a nice correlation ID message to all visitors until YOU the admin who broke everything (euh.. I clicked uninstall... wtf ?!?! ) will FIX IT ! (For free of course.. )
Things that can get left behind (also after the neat uninstall says "finished":
- Event receivers (in every single site (collection) !
- Web Parts
(web part gallery)
- Setup Files