
Many Tears definitely, but just ask any rescues - not all of them do it but a lot do, and some rely entirely on fosters.
I've done it - not for me ultimately but if you like it, it's well worth it.
You can also try nipping onto Dogpages - they have a volunteers forum where you can do a post about yourself, what you can offer, the sort of dogs you can take in etc and there are often threads on there asking for help fostering.