All of these caveats have been known since MongoDB was first invented so not sure why you would use it for several years and THEN decide to switch. And they ar

All of these caveats have been known since MongoDB was first invented so not sure why you would use it for several years and THEN decide to switch. And they are being addressed. For example the global write lock is now only per database and the next release it will be per collection. Likewise map reduce is an ongoing area of improvement. Not sure how Hadoop integration reflects badly on this. Anyway many of those points are design decisions so if your needs aren't being satisfied use something that will work. God knows do your research before deployment because switching is going to be a lot of work.