Operating systems on SD cards

I was getting some wild ideas the last days, like putting some operating systems into SD cards rather than on my hard drive. I'll go further into details now and explain what lead me to consider this probably abominable decision.

I am on a laptop (that means I have a native SD-card reader) which is currently running a cross-distro setup, with a bunch of Linux systems (placed in dedicated ext4 logical partitions into a huge extended one) regulated by an unique GRUB. Since today, my laptop haven't even seen any Windows system with binoculars. I was thinking about placing all the os part of my setup into a Secure Digital to save all my 500 Gb Hard Drive for documents, music, videos and so on, and being able to just remove the SD and boot my system into another computer too, as well as having the possibility of booting other systems into mine by just plugging in another SD, without having to keep it constantly placed in my PC. Also, in the remote case in the near future I just wanted to boot Windows 8 in it, I read it causes major boot incompatibility issues with other systems by needing a digital signature in order for them to start. By having it in a removable drive, I could just get rid of it when I'm needing him and switch its card with Linux one, and so not having any obstacles to their boot.

Now, my questions are: I know unlikely traditional rotating disk drives, integrated circuits ones have a limited lifespan in terms of cluster rewriting. Is it an obstacle to that kind of usage? I mean, some Ultrabooks are using SSD now, is it the same issue, or there are some differences between Solid State Drives and Secure Digitals in that sense? Maybe having them to store system files which are in fixed positions (making the even-usage of cluster technology useless) constantly being re-read and updated and similar things just gets them soon unserviceable, do it?

Second question: are all motherboards and BIOSes able to boot from SDs just like they are from USB pen drives (I mean, provided card reader is USB-connected, isn't it)? Or can't bootloaders like GRUB be installed on SDs working? If they can't, is it a solution installing GRUB to MBR and making boot option pointing to SD? Will it work? Are there any other problems to installing OSs on a Secure Digital?

a limited lifespan in terms of cluster rewriting. Is it an obstacle to that kind of usage? I mean, some Ultrabooks are using SSD now, is it the same issue, or there are some differences between Solid State Drives and Secure Digitals in that sense?

Yes and no. The same problem exists, but an SSD has a controller which does quite a few things. Wear leveling is one of them.

If you use a plain SDcard then you will have to take care of this in another way, e.g. by using a filesystem specifically designed for flash. (Wikipedia page with a list of filesystems used on flash). An other alternative is to just use flash as a backend in combination with a RAM drive. (Boot from flash, initialise RAMdisk, copy from flash to ramdisk. Run OS from RAM. Write changes only on shutdown).

Are all motherboards and BIOSes able to boot from SDs just like they are from USB pen drives (I mean, provided card reader is USB-connected, isn't it)?

All motherboards I tested boot from USB (regardless if it is a USB pen drive, or a USB drive with the flash on a SD card rather then directy soldered on it.)

If you have a laptop with a fully integrated SDcard reader (e.g. not via USB) then things might differ.

Are there any other problems to installing OSs on a Secure Digital?

Some SDcards are quite slow. Check reviews before you buy and get one with low random access times and high IOPS. (The difference between these can be quite big. For an OS access time is important, and as you can see here, those vary quite a bit)