Absolutely.

I know managers who handle 50 - 75 projects at a time. Its a matter of having the right processes, tools and techniques.

At our web design and development agency we do it all the time. In fact, we have one main project manager who manages all of the larger projects. Then we ask our developers to act as project manager on the smaller projects. The managing of multiple projects is good for experience and exposes the project manager to different types of work. It also keeps them from getting bored of working on the same project day in and day out. As for the developers, getting them project management experience is a great way to cross train them and improve their resume.

I think it depends on the size and phase of the project, the experience of the project manager, and the strength of the project team.

I've handled multiple projects and programs. I've found it much easier if the projects are not all initiating or planning at the same time. That said, if you are managing multiple projects, you will need to trust your team.

Yes, you can work on as many projects as you can handle.

What counts is that you achieve the objectives of the projects.

It is actually quite common for project managers to work on more than project provided the projects are small enough to manage.

One common problem in project management is for a project manager to have more than one project and one project taking up too much time meaning that the other projects suffer. This is particularly an issue as projects change organically sometimes significantly increasing their required time input from the project manager in a very short space of time.

One of the key roles of a project manager is to enable and direct the rest of the team who are actually doing the work to deliver the project. If the project manager can not commit enough time, the project can therefore very quickly run out of control in terms of time, cost, quality or many other issues.

In order to do their role well, a project manager must have free time for discussions with the team and the client, and to deal with any immediate issues that turn up. There is therefore every temptation to overload a project manager because there particular workload should often be slightly lower than the rest of the team in order to ensure that they have this spare time. Whilst it may therefore be necessary for project managers to have more than one project, when they are small, it must be done with caution to ensure good performance from the project manager.