I've been using the Nexus One as my main phone for a while now and it turns out to be pretty solid device. It is however not without it's fair share of issues. Here's a few things that Google could fix to make it an even better phone:

• Fix the WiFi dropout issue - the problem is well documented and many bug reports have been filed. The fall-back connection when WiFi drops out is the 3G connection of which I have limited bandwidth and would cost extra dollars if I was to solely rely on this.
• The microphone occasionally cuts out on receiving a call. This is an odd one. It doesn't happen on every call however it happens often enough to warrant a mention. Interesting fact is that when the caller hangs up after not hearing me answer and immediately calls back again, all is well. My most frequent caller, my wife, knows it well enough to not spend too much time on the first call and just call back again.
• OK, this one is not specifically about the phone itself but the Android marketplace. There has to be a better way to browse and sort through the applications. A desktop client would be a good start. A language filter would also assist in finding apps that I would want to use.