After getting excited watching the Google Wave demo video, I signed up for Google Wave developer account. I finally got an invite today morning and I here are my first impressions about Google Wave. 
It is still in Alpha
Or to put it in Google’s words, it is a developer preview account. There is lot of rough edges and occasionally you get warning about wave exploding. 😉
Real-time Inbox
Your wave inbox updates in real-time, much like your gmail inbox, but it somehow distracts you when you are quickly going through the list of waves. May be the list view (which is not available yet) will be less distracting.
Hosting your own wave server through Google Apps
The sandbox account is hosted on Google Apps. So this implies that you can have your own wave server installed in your domain using Google Apps like hosting gmail in your own domain.
Better in Chrome
In my limited testing, I found out that Google wave is really fast and stable in Chrome. Firefox 3.5.1 crashes when I leave Google Wave open for some time due to the large number of AJAX calls made by Google Wave. But in chrome it gives a nice error message.
I guess Google Wave might increase Chrome’s market share 😉
Real-time chat updates
The one feature which excited me more when watching the Google I/O videos was the real time chat updates and now I am much more excited after experiencing it first hand.
It will surely reduce the time you take to reply by more than half. The updates are very fast and it updates for every character typed. I tried it with a FriendFeed friend, and I was able to type the reply before he could finish it.
But I am not sure whether everyone will be excited about it. It clearly exposes the speed and accuracy of your typing skills. Like how body languages and mannerisms expose more than your words in a face to face conversations, the way you type (and correct) your IM message might expose more than the words. So you may have to be careful when you are saying the truth 😉
Folders not labels
I was actually very surprised, when I found that Google wave has Folders and not labels like Gmail. But a little digging showed me that each wave can have a set of tags associated with it. I guess these tags will be visible to everyone who has access to that wave. 
Right now Google wave doesn’t have automatic filters to assign waves to folders like gmail, but I guess they might be added in future.
Extensions, robots and Gadgets
There are lot of Extensions, robots and Gadgets available already. Most of them are created by non-Google developers. You can find some of them at the wave sample gallery. Most of them have their source code, which will help more developers to create their extensions.
Adding a bot to a page is as simple as inviting someone else to the wave. You can see the Tweety the Twitbot in action below.
Playback
Playing back a wave is really awesome. I am able to play back each and every change (even typing corrections) made to the wave by everyone. You feel like watching your actions back.
Will it replace email – may be
After playing with Google wave for sometime, the question which came to my mind is, “Will it replace email”. Google Wave is not just better than email, but much more than that. But the question is, will every one need all the new features. And also it doesn’t mach well with email metaphor. Most people still treat email like postal mail, a one to one conversion. But Wave is more about many to many conversation. So it might take sometime for the mass outside the nerd crowd to accept it.
So will Google wave replace email? May be. Only time can answer. 🙂
