It is, essentially, iMessage for Android. Except that it is browser-based, meaning no matter where I am, or what platform I am using to connect to the web, I can check my text messages. This, to me, is the first very stable reason that would mean I would never contemplate switching from Android.
I am not a fan of SMS. In fact last year I wrote a blog entry on the topic (sadly, I can no longer find it...), yet people still insist on using it. Using it a lot in fact. But for me, I find replying takes time and not something that is efficient and in any way enjoyable, especially not when I am sitting in front of a computer. If that person uses Twitter, or Facebook, and I am sure that they will get the message on their phone, I will always switch to one of those services. Nothing to do with cost or signal coverage, purely due to the fact that I can use my trusty keyboard and type a message in literally 1/100th of the time.
Mighty Text has finally offered me a way to do this. So, to all my SMS-using friends, this is great news... I will actually be replying in a much quicker fashion!
Of course, there are little things that need working out. It only syncs with the Google account, and only Google contacts. If you are like me, with many contacts on the Sim (from older phones, perhaps) or even using service such as Facebook to store contacts and numbers, those will not appear (they will always appear as messages, just names may be missing). There is also an issue of not being able to send group texts to more than 3 people (but the amount of times I do this is very small... New Year and Christmas?) It also isn't the nicest-looking of apps at the moment (it isn't ugly either), but it gets the job done - that is all I care about.
Oh, and it also shows you who is calling and allows you to dial number from the web app as well. All in all, I think it is safe to say... I'm a fan.