In this day and age especially, superheroes trying to keep up secret identities doesn't make any sense. The narrative excuse is usually that it's so the hero's loved ones won't be targeted by their villains, and the meta-reasoning is that it's easier for readers to identify with a dude in a shirt and tie working in an office than when he's flying about saving the world in a cape and tights. Neither of them stand up to much scrutiny, though, because plenty of hero's friends, family and lovers have fallen prey to bad guys' nefarious plans, and if we'll readily accept an alien from a dead planet coming here and shooting lasers out of his eyes, why would we wanna see his boring day job? As for the "this day and age" thing, do you really think it would be possible to maintain a secret identity with the proliferation of paparazzi culture, social media and camera phones? Celebrity gossip filters out through any number of leaks, people catch criminals by taking photos on their iPhone, even state secrets get proliferated through Twitter. Spider-Man just needs to get changed in the wrong alleyway for his mug to be plastered all over the Daily Bugle.
Tom Baker is the Comics Editor at WhatCulture! He's heard all the Doctor Who jokes, but not many about Randall and Hopkirk. He also blogs at http://communibearsilostate.wordpress.com/