Someone mentioned that adding items is difficult--not true in the latest version at least, which can import/export csv.
The only real issue with VirtueMart is that it is a work in progress and thus missing some features that other free solutions like Zen Cart provide out of the box. I found many tweaks and mods in the growing forum but the fact there are that many of them spells the shortcomings of the core code. If you don't code, before you opt for VirtueMart, make sure it supports all or most of the features you need. The forum will not help you much if you can't code.
If you have some tweaking experience, you can indeed do a whole lot with VM as I found it to be quite flexible.