I just ordered myself a g400 from amazon. I see the g500 is getting a lot of love around here, I hope I didn't make the wrong selection!
I do not think you did. The g400 has the better sensor without acceleration. It is less picky about the surface it uses, it is not as heavy as the G500 (which you can add weights to, lolwut?) and the weight is more evenly ditributed. It does not have a sensor that is placed towards the front instead of being centered, which affect how the cursor respond to wrist movement. It also does not have the annoying wobbly scroll wheel that is almost impossible to use in a gaming situation (hard to click without accidentally left and right scrolling etc.).
All in all, I would say you made a good decision.
I was wondering why an optical sensor is preferred over a laser? is that just for gaming? the g500 and now the g500s has suited me fine for non gaming usage or so I think. am I missing anything?
Almost all modern sensors have enough DPI and a high enough max tracking speed to satisfy even very demanding gamers. So what really matters is the accuracy and reliability of the sensor. This is where the optical sensor shines, though it is not as quantifiable that you can advertise with it on the box (like 8000+ DPI regardless of how useless it is to 95% of consumers). Both newer laser and optical sensors typically do not have prediction. However, all current laser sensors have acceleration to an extent. People differ in how much they are bothered by this, and some claim that if it is consistent, you can adjust to it. However, why deal with it in the first place? I think it is telling that sponsored teams practically refuse to use their sponsors flagship models (typically heavy laser mice) , going as far as using mice from the sponsor that are not even currently in production anymore. Laser mice are almost non-existent in the competitive scene. I thought it was pretty notable that one of the members if NIP's Counter Strike team (sponsored by Steelseries) listed the Sensei as his mouse, but that has since been adjusted and changed to the Ikari optical....
Laser sensors typically also have more issues when used on different surfaces. When the Avago ADNS 9500 came out, there were a lot of complaints about negative acceleration on cloth pads. Newer incarnations of the sensor in mice like the Sensei may have gotten rid of this issue, and the newer 9800 sensor may have gotten rid of it completely ( I am not sure), but for now I will just stick with optical sensors until such issues have been addressed for sure.
One thing to note is that these issues generally become more apparent as you use a lower sensitivity, relying on large fast and accurate swipes (flick shots and the like). These tend to really amplify and expose the problem. If you are a person playing Starcraft 2 on high sensitivity, none of this will be an issue for you.
