How good are USB memory sticks for running operating systems from, and the ones based in micro sd cards?

They are so good that people run OS from them. Try out knoppix and see if you like it. If the PC boots from the media it doesn't matter that much which one you use. I haven't tried sd cards. CF cards work fine.

The only issue with the sd cards is the readers that have to be used. Not all work as expected. Consider a usb flash drive for more consistent results would be my guess.

No flash can last as long normally as a hard drive, yet.

See pendrivelinux.com and others for ways to install and run.

It used to be that it was a hit and miss deal on some usb flash drives. Some tools may have helped a lot like the HP but not all could be made to boot. Almost every new flash can be made to boot but look for sales info to confirm if in doubt. Many advertise the ability.

I think the usb flash drive installs have a use for me and I use them a lot for more portable reasons or test reasons not ever day use.

The times I do use compact flash is for older stuff with an ide to cf adapter to make reloads fast as changing a cf.