I'm trying to understand better the concept of bluetooth dongles v2's
usage of multiple devices before I buy one, so I'm dividing this to
small questions:

First and foremost, is it even related to the brand as long as it's v2?

See, locally I've found only two such devices:
1) Qstarz BD-Q371 USB Bluetooth v2.0 Dongle
http://www.qstarz.com/products/bd-q371.aspx
2) EDIMAX Bluetooth V2.0 USB EDR Dongle EB-DGC2
http://www.edimax.nl/html/english/products/EB-DGCX.htm

One store that sells the former told me it can connect to "unlimited
devices...as long as you create a profile for each".
One store that sells the latter told me casually "up to 7 devices and no more".
Neither store managed to elaborate further what makes them think it
supports either "unlimited devices" or "7".

I find it hard to believe 2 devices that do the same thing and cost
about the same amount have such an amazing difference - "unlimited
devices" ("as long as", etc.) vs. "7 devices".

So which is it? 7? Unlimited? Identical to the number of profiles?
If it's the latter, it makes no sense as the "7 only" latter seems to
have even more profiles according to its official page if you count
the "Profile Support"...

With that out of the way, currently I have a dongle v1 and a bluetooth
cell phone. With XP SP2, I never even bothered to install that dongle.
All I did was detecting the phone and from then on I just use the cell
phone's free software offered online.

So how will this change if the first store was right about the "profile
for each device" concept? Can I keep just SP2's driver? Can I still
use my cell phone and also buy and totally ignore whichever Bluetooth
probably v1 dongle that comes with, say, Microsoft BT Keyboard &
Mouse and use all at the same time (if so, under what profile for
each?)?

Thanks!

First , we need to know what is Bluetooth V.2:

 - Bluetooth V.2 is the latest version of Bluetooth. The main
improvement over Bluetooth 1.0 is that V.2 (being backwards compatible
with 1.x) is nearly 3 times faster than its predecessor, and in some
cases up to 10 times - V.2 it's not part of the brand.

Second, we need to know (basically) how does a Blueetooth coneection work:

 - Think of "bluetooth devices" as "persons", and "profiles" or "list
of services" as "abilities" that those "persons" are capable of.

 - When you meet someone, and you give away your contact card and
receive theirs, you are establishing a trusted relationship - that is
called pairing devices.

 - After your "met" you can make a inquiry to that person, for you to
know her abilities - now you know which services are your bluetooth
devices capable of.

 - So, you are in a conversation with the new guy, and you discover
that he plays baseball - just like you. Now that you know that, you
can play together. Like that, if you want to make calls in Skype using
your bluetooth headset, you should verify if booth dongle has that
service, and then you should create a profile for that. Or if you wish
to connect a mobile phone to a computer to send that lovely sunset
photo you took, just find out which is the right service, and then
create the profile, so they can connect.

Some devices can establish many connections at the same time with
other devices (like your computer connected to a mobile phone modem, a
bluetooth headset, and to another computer - the usb dongle is
conected with 3 different devices at the same time). Other devices can
only handle one connection at a time. But you can have as many
different devices paired (your device "remembers" other devices it has
"met") as many persons you can meet - or let's just say, unlimited,

In your specific case, I think that the seller who says "up to 7
devices and no more" is referring to "instant connections" - the
dongle can connect at the same time with 7 different devices. The
other seller must be talking about with how many devices you can pair
your usb dongle - unlimited.

About the hardware question, when you buy your new bluetooth dongle,
you should have to pair it with your keyboard / mouse, in order to the
computer recognizes it.

Sorry for the long text :)

Thanks! However, obviously I meant "at the same time". So my question
is how many devices at the same time can v2 support? 7? Or does it
depend on the brand and just the one mentioned above specifically
supports 7? And in that case, is there even a way to tell by looking
at the pages above?

As for they keyboard and mouse, I know that. But as far as I
understand, they usually come with 2 limited v1 dongles and I wonder
if I can just use the v2 one with both of them (and while at it, also
simply using SP2's driver).

Sorry if I've misunderstood you. :S

Well, at the same time you can have 1 device be connected to other 7
devices, say as if one's the master and the other are slaves, ok? And
this is like that on all Bluetooth versions (V1, V2).

About the keyboard and mouse: as long as you buy a bluetooth dongle
that supports HID service, they will pair and work with your computer.
And yes, you can use SP2's driver. Personally, I would rather use the
driver that comes with the new bluetooth dongle, because it gives you
advanced control over it.

This is where you're wrong. Bluetooth v1 supports just 1 on 1
connections and that's its biggest limitation. The question is how
many connections does v2 support at the same time. You claim 7, but
where did you get this number from?

Who needs the advanced control of this driver? The cell phone works
with a special program anyway and the keyboard and mouse just do their
thing.

I have a friend named Wikipedia :P search for Bluetooth and look for
"Communication & connection" (don't get me wrong, I know that it's not
always 100% accurate).

The SP2's driver is made to work with a wide range of bluetooth
dongles. So I think that you can get better support using the original
driver. But if the windows' driver works, and you prefer it, you're
free tu use it :)