Android: Serializable Considered Harmful
This is an old problem, but anyone I can convince not to use Serializable on Android will help the system as a whole.
There is some data saved between launches of my application - a list of complex objects. When I first learned Android I assumed that the fastest way to get the app up and running would be to slap Serializable on my data classes and call it a day. It certainly got things up and running quickly, but with some serious performance issues. I never noticed this in early testing because I only saved a few objects at a time. However, when I got up to 5+ objects the system started to slow down, and at 10+ it ran like molasses. There's not normally that many objects, but it's still something to be concerned about. It's not like I was doing anything complex, however - it was simply that Serializable is that slow.
Not only that, but I had to live in constant fear of changing the data structure. If enough things changed I would have to write my own serialization processes to work with backwards compatibility. Yuck.
I switched to using JSON to store all my data and this decision has made my life so much better. Android comes with a good JSON library and it's pretty simple to add JSON support to classes. JSON is much, much faster than serialization and comes out with much smaller results, too (you can even GZip the results to make them smaller still). To put it in perspective, the save time is now unnoticeable, whereas I could count the seconds using Serializable; and the file size was reduced by an order of magnitude.
Not only is it better for saving data, it's a very easy way to pass data between components. When I first started, I saw three ways to pass data between components: Serializing, parceling, or storing data in the Application context. Serializing was proving too slow, parceling is really a pain in the ass, and the last solution is harder to integrate with later on (no one else can call your component). JSON has proven a much better solution - it's fast enough to get by, but not nearly the pain in the ass that Parcels are.