it's great. i'm in a new relationship with one, and i LOVE it. i think there is another thread on this somewhere... i would do a search. i remember CC talking about her experiences with an istp.
my istp is laidback, relaxed and doesn't take any of my emotional tirades to heart. he just sort of rolls with the punches, laughs at me and enjoys my company. he's also really deep and interesting--which surprised me at first cause i thought he would be so "in the moment" that he wouldn't wonder about things he could not see... on the contrary! he likes picking my brain about things and asks a lot of questions.
he's also good for adventures and is spontaneous like me! whee!
and, also surprisingly, it seems he wants to be around me as much as i want to be around him. i thought istps were known for their need for space, but this one doesn't really need it anymore than i do. could just be cause he likes me though. i get the sense he doesn't spend time with many people.
it's a low pressure relationship, feels more like a friendship at times, but is really a lot of fun. i think the only downside might be the fact that neither of us will pay bills on time... and him being more introverted than me. although, again, he has stepped up to the plate and met all of my crazy friends (which could just be him trying to make a good first impression since the relationship is new).