Yes, it's time for another semi rant. Now, I like pseudonyms, I use one myself. But I understand there are limitations to using a name that's not your own (for example, it's hard to friend people on facebook if they don't know your real name).
In the past pseudonyms were chosen for a few reasons: because the author's name was the wrong gender to match their genre (or, historically, just by women trying to get their books sold period). That's why a lot of female SF writers use initials, and why some men writing urban fantasy do too. Or they were used to differentiate writing between genres (so Nora Roberts writes romances but J. D. Robb writes mysteries). Or because the author's name was unpronounceable or otherwise unsuitable and so a nom de plume was used instead. *
That's no longer the case. More and more frequently I'm finding 1) authors whose first series didn't do so well so the author's forced to change names to start over, hopefully building a following under this new name. And 2) authors who use a new name per inter genre series (ex: Alayna Williams and her alter ego Laura Bickle both write urban fantasy).
Why is this a problem? The obvious reason is that it doesn't allow authors to build an audience. Sure, people might not have flocked to your first series, doesn't mean they won't like your next one - and liking it, go back to read your first. In other words, you lose repeat business by making it hard for readers to know what else you've written. This is why some authors works are later republished with new covers, clearly stating the author's real name (Dawn Cook's books now advertise that they're written by Kim Harrison, so her urban fantasy readers will pick up her traditional fantasy novels). Jim Hines has done some great posts about how much his books and ebooks have earned. His Goblin books have sold less than his Princess books (I'd say the increase in sales for his newer books is because his writing has improved over the years and the Princess books appeal to a wider audience, as fairytale retellings are becoming increasingly popular again). But for his Princess readers to pick up his Goblin books, and vice versa, they have to be next to each other on the shelf, not hidden under some other name elsewhere in the store.
The other problem with changing names per series is that readers are often hesitant to try out a brand new author. They want to know that the author is capable of finishing a story (trilogy, etc.) and often wait for word of mouth recommendations. If you're constantly a debut author, there's little chance for word of mouth to help you (unless you're one of those freakishly lucky souls whose debut causes ripples on the internet and beyond so everyone's looking for your book). This is even more crippling if your book debuts in hardcover (VERY few people will pay hardcover price to test out a new author, especially in today's economic climate, unless they've got an amazing marketing campaign or celebrity endorsement of some sort).
Working at a bookstore, I like to showcase new SF/F authors - those with 3 books or less. It's become increasingly necessary for me to google new authors to see if they're actually new. This is even more challenging for my SF Signal New Author Spotlights, where I'll disqualify someone if self-published books push them past the 3 books limit (ie, if they've got 1-3 professionally published books and I discover they've self-published several others, they no longer qualify for that post).
Most surprising, and frankly disappointing recently, was when Joe Kimball's debut novel, Timecaster came out. New SF authors are few and far between (though they seem to be increasing :) ), so when one comes along I look forward to showcasing them. Seems Mr. Kimball is another name for J. A. Konrath, which surprised me as he's been doing so well with epublishing.
Ultimately, it's getting to the point that if you like someone's work, google them. You may discover they've written something else, under another name.
Addendum: I've started a list of author pseudonyms so that when someone asks at the store for recommendations, I can suggest other books by the same authors.
* I came up with 2 more reasons people use pseudonyms after writing this post. The first is for anonymity - especially when writing erotica, the second is to get around contract language that states you can only publish with one publisher at a time, thereby reducing the number of books you can get out a year. By writing under a second name, you can sell two series to two different publishing houses.