What problems have you had with it ?
In my fairly long experience of using it, it's cheap and effective if you configure it and test it properly.
Now, would I rely on it to control a mission-critical application ? No. Would I rely on it to unlock my outer doors ? No (and not on any other protocol either). Would I rely on it to control my lights and switch on a coffee machine ? You bet.
I think that's what the original poster exemplified.
The main advantage of X10 is that it's simple, versatile and inexpensive dead easy to extend and needs no additional control cabling to be retrofitted. The downside is mainly the cheap quality of the components unless you get the professional ones.
I would agree, that to do a proper 100% reliable automation system you need to implement something like C-bus, although that requires independent control cabling (as opposed to its near namesake cebus, which is power line carrier based). Both are considerably more expensive of course. I've looked into Z-wave too, but that also gets pricey and as far as I know, has fewer applications available. Rako is even more expensive. If I were building a new house, C-bus would be the way to go, but even its distance remote access isn't as secure as you may like, and I doubt that many implementations adopt it.
Which of the newer protocols would you adopt personally ?
BTW - if you want to prevent individual power outlets from controlling X10 devices, you insert a filter which removes the control signals.