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http://twitter.mailana.com/ has been in the wild for a week now, and the best part has been hearing from users. I'm only human, so of course I love it when people tell me how well it's working; but as a developer the best comments are the complaints. Here's an example of why they're so useful.

I have a search filter set up for Mailana so any Twitter messages mentioning it show up in my RSS reader. On Saturday evening I spotted this from @mayaREguru

That Mailana thing is way wrong wrong wrong and weird. Makes no sense at all

The first thing that caught my attention was that she wasn't just hitting some minor glitches, it sounded like it was completely broken for her. That made my ears perk up, because if others are hitting similar problems it will be ruining a lot of people's experiences. Most of those people won't complain, so a single comment likely represents tens or hundreds of unimpressed potential users.

I got in touch with Maya and she gave me some more details. The whole BFF list was showing up incorrectly, with a lot of people she frequently talked to missing, and other people she'd only exchanged a few messages with listed instead. It's actually a lot easier to debug a massive problem like that than something more subtle, so I set to work figuring out what was going wrong.

Mailana works by mapping conversations. To know what conversations someone's had in Twitter, I need to import all the status updates for both sides of the conversation. That means for any user, there might be hundreds of other people they've sent @ messages to, and I need to download all their status updates to discover if those other people replied. When a new graph needs to be generated for a person, I first grab all their own messages, and then import all the messages of everyone they've sent messages to.

When I looked at Maya's information in the database, I could see there were a lot of people she'd sent messages to who hadn't been imported, so as far as the system was concerned she'd not had conversations with them, since it never saw any replies. I ignore those one-sided exchanges, since I'm looking for real relationships where there's two-way communication, so all those unimported people weren't showing up in the list or the graph.

Now I knew the immediate cause of the problem, but I had to work out why those people hadn't been imported. I won't go into the gory details, but after some debugging it turned out a crucial bit of code was looking at the wrong piece of information when figuring out the list of people to grab messages for.

It turned out my initial guess was correct, the same problem would have affected a lot of people's profiles. So by fixing Maya's graph I solved it for them too.

The issue never showed up in my own testing and I'd still be silently losing potential users still if I hadn't heard from her. That's why bug reports are like gold dust.

When I was working in the game industry writing tools for artists, I'd literally be sitting back-to-back with my users. Being that close to my customers made me feel their pain (and hear their cursing). That guidance helped me produce the programs I'm proudest of. Knowing they could turn around and slap me on the back of the head when it crashed concentrated my mind wonderfully!

Thanks to @mayaREguru, @robertshippey, @aleferreira and everyone else who's told me about things going wrong. Keep the complaints coming, it's really helping me improve Mailana!