Please tell me, if you know, how much
faster is Windows/Linux on BootCamp
than on Parallels/Fusion
It's hard to quantify without any kind of benchmarks to definitively answer your question. In my experience with both bootcamp and vmware fusion (or parallels/virtualbox) for me it was a convenience issue more than anything so I use vmware fusion on a regular basis. Performance was noticeable between dual-boot and virtualization but it depends on how you use your computer.
Software development (Visual Studio,
Eclipse, Notepad++, Total Commander,
Git Bash etc.)
I use Visual Studio 2008/2010 on Windows 7 Pro (64-bit) and KomodoEdit on Ubuntu. I don't see any real development issues other than a slightly longer build time. If I'm building an ASP.NET site, getting IIS to start up is a little longer than normal but nothing that is noticeably worse than usual.
I can't speak for VSS/TFS/Git/CVS/source version control, etc. etc. Basically, software development would be nearly identical but depending on the complexity of the code, libraries/assemblies, dependencies and such, the compilation process may take a little longer than normal. Again, benchmarks will really show the difference but in my experience it's close enough to non-virtual environments.
Live TV (Windows Media Center with my
USB DVB-T TV Stick)
I've never watched live TV via USB or in a virtual machine so I can't say anything for sure. But even watching streaming video or video files over network share, the lag at times was noticeable. Anything I/O heavy you will notice more so using any virtual environment.
Games (Quake III, Dragon Age, Unreal
Unless you plan on playing solitaire, I would stay away from virtualized games. I tried playing Civ4 on Windows 7 with 2GB of RAM and it was too damn slow. I can't imagine Quake, Unreal Tournament being much better. Granted those games are relatively old, I just don't think serious gamers can expect virtual machines to perform on par to native hardware.
Utility Software (Nokia Ovi Suite for
my cell, Lingvo dictionary etc.)
I think this will run as expected like a non-virtual machine.
Linux (Ubuntu 10.04 for testing and
debugging software I develop)
It'll be close to non-virtual machine speed.
There's a way to virtualize a bootcamp partition which may be what you're looking for. If you create a bootcamp partition, install windows, and boot into OSX, VMWare Fusion has an option to treat the bootcamp partition as a VM so you could in fact run either native dual boot OR virtual machine instance. This might be the better way to go if performance is of the utmost priority.
Install all the software and games you want. If they perform poorly in a VM, then at the least it's on your bootcamp partition. If games/apps/tv run fine then you have the flexibility to use OSX and switch to Windows 7 whenever you need it. I do not know if this can work for Linux but it wouldn't surprise me if there was a way to do it. Here's a link to VMWare's info on doing such a configuration.