My biggest advice, use rails plugins sparingly, and when you do ensure they are well maintained. Nothing is worse than an old rails project that is using 20 plugins and you need to update it to a new major version of rails.
So very true. Almost all the misery of maintaining and upgrading a Rails app comes from the interactions between plugins, each other, and Rails.
Why is this? I don't know exactly. It could be the way that plugins tend to manipulate multiple layers of the stack and tend not to use clearly-defined public interfaces. I suspect that more of it is the fact that plugins are the self-promotion tool of choice for the jobbing Rails developer: they fall from grace as quickly as they rose, abandoned by the developers to whom they gave a leg up, supplanted by a new, different plugin with an obviously - everyone agrees! - much more correct way of solving the problem. Meanwhile, your old Rails app is dependent on a dozen pieces of decrepit abandonware.
Monkeypatching! It's all fun and games until someone else decides that monkeypatching #poke is also what their gem or plugin needs. Then, of course, you start accidentally #poke'ing your Eye when you least expect it, and cannot figure out from where or why...
My biggest advice, use rails plugins sparingly, and when you do ensure they are well maintained. Nothing is worse than an old rails project that is using 20 plugins and you need to update it to a new major version of rails.