Yahoo is a case study in how to do everything wrong by not caring about what your users want. A lot of tech companies make similar mistakes, but Yahoo seems to be the only one with enough capital to do it repeatedly. I've always found instant messengers interesting ever since I wrote a spam filter for Pidgin quite some years ago, so my ears perked up when I learnt that Yahoo is re-launching Yahoo Messenger.
With the rejuvenation of Yahoo Messenger, Yahoo is now playing catchup with a product that they've had for 17 years. They've largely ignored it for the past five, so their position somewhere at the lower end of the market is entirely their own fault. The way they seek to reassert their position is to appeal to new users, who are almost certainly already using a comparable service, while telling existing users they must change to fit the new vision. This will not work.
This may be a surprise to most tech hipsters, but many people still use Yahoo Messenger (and there is demand for desktop instant messaging applications). Maybe not as many people use it as they did 5 years ago (at least in part due to Yahoo's neglect of the product), and maybe not as many use it as use the newer mobile based messengers, but there is a core user base who use Yahoo Messenger because it remains convenient and useful.
The existing Yahoo Messenger distinguishes itself from most modern instant messengers by being a well featured, stable, and (reasonably) resource light desktop application. Web applications are often useful, but sometimes a desktop application is better and an instant messenger is one obvious place, because it easily ties the on/off or idle state of your PC to your availability, and real time messages come through passively while not getting lost in the noise of your other browser tabs. Desktop based social apps are still a good and sensible way to compartmentalise your life and control your own availability.
The new Yahoo Messenger is not the same product as it was, and does not solve the same use case. It is different in that it:
1. It doesn't retain your old contact list. I can't overstate how stupid this is. When Gmail next releases a new major version, I don't want to sign in and find out all my existing emails and contacts no longer exist. When Facebook releases its next major version, nobody wants to sign in and find all their friends have vanished from their page. Dumping the old contact list is simply idiotic - most people will sign in to an empty page, say "oh", and close it. It no longer works for them. This is astonishingly stupid.
2. Is not a desktop application; it's web and mobile only, which will interfere with how existing users want to use - mostly they don't want to use it - they just want it to be there when they're sat at their PC.
3. Is not an instant messenger. This is crucial. With a very minor UI change, the app is no longer designed for real-time conversations, it is designed to broadcast a message to a person and hope they pick it up and reply at some point in the near future. This is evident in the fact they don't provide an online status for contacts, so you can't choose to talk to someone that you know is available. You have to guess. And wait. It has more in common with email or text message. This represents a fundamental change in the dynamic of the users' interaction with each other, and so existing user's expectations no longer match what they experience.
Yahoo's strategy here is presumably to poach market-share from other similar mobile messaging apps. There are a lot of other mobile messaging apps, so it's a big market with lots of potential users.
However, they are late into the game and won't succeed in displacing any of the existing players because the new Yahoo Messenger doesn't have any strongly compelling advantages (gimmicky features aside, it doesn't make it easier to communicate with your friends), so Yahoo provides no real incentive to move away from other similar apps.
With this comes the seed problem - they have no apparent strategy to seed an initial user base. Seeding a user base is a difficult chicken and egg problem - nobody uses your app because nobody else uses it - but Yahoo is sitting on a huge advantage here which they are squandering: they already have existing users! Perhaps they are relying on their existing users migrating and re-establishing their own contact lists. Yahoo will be very disappointed if this is the plan.
I don't disagree that Yahoo Messenger is in desperate need of some kind of relaunch, but Yahoo is going about this all the wrong way. What they need to do is modernise the existing messenger while catering to existing users' requirements, not to change its focus to a different use case. They need to insert status indicators; an almost trivial change to ensure that the app remains focused on real time communication, and they need to make the existing desktop client at least basically compatible (for sending/receiving messages) with the new app. This would give them a significant stable user base at day 0, and for the future, those users need to be able to update to the new version and continue to use it with roughly the same pattern as they did the old version.
The new app will alienate their existing users while failing to acquire more. The end result of this is that Skype will see a short term bump to their sign up figures as existing Yahoo Messenger users are forced to migrate, while in two to three years time, Yahoo will have even less presence instant messaging.