Update: imo is dead!
There are plenty of instant messaging apps for Android, and there's something wrong with all of them. They either suck your battery dry, don't chat with Skype, or they won't let you use multiple accounts on the same network. And even if they get these things right, they show obtrusive ads that even AdFree can't block. Or they ask for money. I know programmers need to eat too, but instant messengers are like web browsers: nobody pays for them.
What makes imo good
Instant messenger imo is one of the few chat apps that works with Skype. Of course it also talks to the usual suspects: Google Talk, MSN, Yahoo, ICQ, Facebook, AIM, etc. Better yet, you can use as many accounts as you like. Want to sign in with your Google Talk account for work and use your separate Google Talk account for your friends at the same time? Most IM clients will refuse, but imo knows your need for split personalities and lets you log into all of them.
An old imo problem used to be that it would launch itself out of nowhere and sign you back in after you logged out, but so far the latest update keeps quiet when I tell it to shut up. And now it does group chats too! Did I mention its interface got polished up a bit?
To do list
Not that imo is perfect. Its smilies are an ugly shade of green. They're case sensitive too: :-P works, but :-p does not. Neither do :P and :p. Not everybody uses imo, so it should learn to handle the slightly different smiley formats used by different apps and networks. Those with amoled screens might want a black background instead of a white one. The biggest annoyance: whenever you scroll through a chat, imo pops up the question whether you want to enable "chat history" or not. Your only options are "yes" or "not now." They really should add another choice: "no, and don't ask me again."
But in the grand scheme of things those are minor flaws. The shortcomings of the competition are much, much worse. For now, imo is the best Android chat app out there. Yes, even better than Nimbuzz. Although push notifications would be a nice addition to a future version. Maybe one day it will add WhatsApp to its list of supported networks too?
Update: imo is dead!