There's a section in the Epic Level Handbook on Epic Leadership, and it mentions that you can't have a follower of effective follower level greater than 20 (i.e. no epic commoners/experts/warriors, no adepts or aristocrats of level 19+, and no PC classes of level 18+). This sounds like a reasonable rule... until you crunch the numbers.
See, you get a flat +100 followers of EFL 1 per extra point of Leadership score past 40, you get an EFL 2 follower for every ten EFL 1 followers (rounded up), and you get an EFL N+1 follower for every two EFL N followers where N > 1 (rounded up, except that 0.5 rounds to 0). So, what Leadership score would you need in order to get a follower of EFL 21 and therefore trigger the "no epic followers" rule?
You would get 2,621,500 EFL 1 followers, 262,150 EFL 2 followers, 131,075 EFL 3 followers, 65,538 EFL 4 followers, 32,769 EFL 5 followers, 16,385 EFL 6 followers, 8,193 EFL 7 followers, 4,097 EFL 8 followers, 2,049 EFL 9 followers, 1,025 EFL 10 followers, 513 EFL 11 followers, 257 EFL 12 followers, 129 EFL 13 followers, 65 EFL 14 followers, 33 EFL 15 followers, 17 EFL 16 followers, 9 EFL 17 followers, 5 EFL 18 followers, 3 EFL 19 followers, 2 EFL 20 followers, and one illegal EFL 21 follower, for a total of 3,145,814 (or 3,145,815 with the illegal epic follower). For reference, if you took Legendary Commander this would give you about half the population of Han China or the Roman Empire, or 90-95% of the population of Eberron (the whole planet; adding up all the population figures gives about 33.37 million, but there's no population data for Xen'drik outside Stormreach and Dar Qat so the drow, giants and other wilderness inhabitants there aren't included in that number).
Getting a Leadership score of 26,245 probably involves a level somewhere between 20,000 and 25,000; it's pretty trivial for the latter but rather difficult for the former (unless magic item boosts to Charisma are allowed to count toward Leadership; then you only need about level 220 or so, since a Cloak of Epic Charisma +52,000 only costs 27,040,000,000,000 gp and WBL at level 220 is over 383 trillion).
This isn't really a "fun find" in the normal sense of "I'm so taking that", but it's still hilarious and I wanted to share it (as an aside, it does demonstrate how low the population of fantasy worlds tends to be, as Eberron's population is substantially lower than even Classical Earth, let alone mediaeval Earth which had about ten times Eberron's population).