I don't have one to test this at the moment but I plan to buy an 8GB card and use it with ReadyBoost (Windows 7) on my laptop.
No problem with exFAT but whether you can use it for Readyboost really depends on the read/write speed of the card.
Windows 7 automatically tests this for you when you plug it in.
There are workarounds but it kind of defeats the point as the performance would not be good enough to benefit from the extra cache.
Yes to the content of your question, you can format, partition and/or do pretty much anything to most flash memory (sticks/cards).
I am not 100% sure about your title line - exfat, I do not see a problem, but cannot say for sure. If using Readyboost, I would just stick with default FAT.