Well, speaking from experience, I am managing an Energy Compensation Project in Mexico City with colleagues in Germany (for Control and Protection, as well as PM and Procurement) and in Colombia (exclusively for Civil Engineering).
What I found to be the biggest problem so far is that my German colleagues are not used to the level of bureaucracy needed in a Project for the Mexican Federal Government, which has led to a number of misunderstandings and even some tension between the German PM and I when it comes to delivering documentation according to the client's very specific needs (Our client is the Federal Comission of Electricity). Also, receiving the Engineering documentation from Colombia has been a real hassle; even though the colombian contractor charged less than half of what any mexican contractor would have charged (and less than a tenth compared to the germans), the quality standards turned out to be quite low, and the long delivery times have caused us a lot of trouble with the client.
My opinion is that in order to have a "virtual team" working on a project, the entire team needs to standarize the processes of engineering, procurement and construction (especially if both teams work for the same company), as well as the quality procedures in order to avoid misunderstandings like the ones I've had. Also, and this is what I consider the most important thing given a situation like mine, all the parties involved need to be aware of the condition of the client, its needs and its own fashion of getting things done regardless of the cultural differences and time zone. After all, the client pays our bills, right?
An advantage thanks to the difference in time zones in this case could be that if the entire team gets organized, the people from Europe can get the day started and have all the information needed for the day at say 4:00 pm, when the american team starts its day and takes over. This way the entire team extends its work day to 16 hours as opposed to 8. On the other hand, if the team is not well organized, the american team will have to re-do the work delivered by their european counterparts (or vice-versa) and end up paying more than double for the same amount of work done.
Well, I hope this helps. I have so many extra issues I'd like to post about virtual teams but I consider these the most critical to start with.
Cheers!