Hello,
I wonder and hence ask you whether there is a difference in boot time between two systems when just one of them features grub at the boot stage.
Thanks

And what do you think is there if grub is absent ?.

Yes, there is a really big difference. System without grub will boot in infinite time, because it will never boot at all.

Since the question is out there, I'll ask 1 also.

1. If I installed grub2 in it's own partition and load multiple os'es, when the other os'es make entries to the existing grub do they still have grub in their root?

2. If it's not necessary then how do you disable the additional grub from being loaded?

3. Also I've been trying to find out what fs does the grub2 use?

I hope this wasn't too newbieish.

This is a misunderstanding, only one OS will make entries to your Grub-installation, namely that OS that has installed this Grub-installation. You can also install Grub independent from any OS, but the you will have to maintain the entries yourself. Only one bootloader has to been present one the system, so you will be fine if you simply don't install grub on more than one OS.
Grub is only a bootloader, it uses no filesystem, its first part is written to the master boot record, the second must ly on a filesystem that Grub knows. For more infos about bootloading with Grub have a look here.

Thank you TobiSGD the reason I asked is because I had grub-legacy and grub2 recently and found it easier to get rid of legacy and change my 2.6.26 kernel to 2.6.32 so that I could read ext4 fs.
Right now I have three grubs and wins chainloader so, I was trying to find-out what fs was better for grub to read all os'es with simple os-prober. Thank you as your answer was most helpful

Strictly speaking this is true - however I have had an occasion (recently) where choosing not to install a boot-loader also caused the omission of a kernel at all.
With grub legacy, choosing to always install to a partition wasn't a problem. Grub2 however needs to build a node list for core.img - the so-called flexibility has some (normally hidden) costs. grub2 complains if installed to a partition - I haven't found this causes a problem yet, but the possibility is there.
It is always possible that distro devs will take the decision on where (or whether) to install a loader out of your hands completely. SLES for example.

I have noticed it takes grub2 about twice as long to boot a partition as it does grub legacy.