The POD, or Ping of Death, bot is the standard bot for Half-Life's Counter-Strike mod. The majority of waypoint files available for download are in PoD's .pwf format. There are a number of reasons why it has become so popular to the current point of ubiquity. I'll outline them here.
For a start, the navigation skill of the bots is absolutely second to none. Real bot attempted to do away with waypoints, but it's revised state of "optional" waypoints shows that really AI is nowhere near the state it would need to be for this to be plausible. Podbots, on the other hand, for a little extra effort invested beforehand, offer an ability to find their way round maps quite unrivalled elsewhere.
Indeed, in the hands of a good waypointer, the various waypointing facilities built into the bot code make the system both effective and remarkably straight-forward. Waypointing has traditional been a highly-time consuming affair, but Podbot automates it as far as possible and really removes the tedious aspects.
The second reason is the quality of the combat the bots provide. The author of the bots, Marcus Klinge, has now been hired by Gearbox Studios to produce the AI for their commercial venture Condition Zero, such is the quality of his work. Klinge has implemented a whole seperate portion of code for the combat, such that bots use cover, flanking, and each of the weapons and grenades in exactly the way a real player would. I don't think we've yet reached the stage where humans and bots are indistinguishable, however many times I've heard it, but Podbot is certainly the best effort yet.
In the most recent releases, Klinge has also put time into making the bots interact in a more realistic fashion. They use the radio, in a simplistic fashion, and although they can't grasp all the commands you might give them, instructions like "Follow me" and "Fall back" are obeyed (or not) in a convincing manner. There's even an Eliza-style chat system, which provides a little limited amusement once dead.
The reasons that Podbot has ascended to its current height is more than just Klinge's obvious dedication, skill and patience. There's been a healthy community on the Podbot website, suggesting new features and weeding out bugs, for a long time, and the bots' author seems to genuinly respond to the users' observations - even when the answer is "No".
I have no doubt that the bots in Condition Zero will be another huge leap forward from Podbot, a reflection of the vastly increased amount of testing and development time available to a programmer getting paid for his work. It is genuine proof that sustained hard work for an apparently altrustic cause can eventually reap dividends.