Well, I think most of the difficulties my husband and I experience have been mentioned already, but I will add some comments.
Hearing "it's making my jaw hurt" for the thousandth time?
This really sucks. It sucks for me as well as for him. I'm pretty damned good at oral, if I do say so myself (and he says so too), but even I can't go for too long without my jaw getting sore.
That said, varying what I'm doing -- taking it out and licking on it even for just a few seconds, or sucking just on the head, or paying a bit of oral attention to the balls...it doesn't take long for my jaw to recover and then I can focus on his cock again. Good tip for anybody who just gives up when this happens.
Severely limited potential for satisfying oral sex.
When my husband (then husband-to-be) and I first met and were PM'ing on LPSG, I asked him if he'd ever had problems with a woman not being able to take him. By and large (no pun intended), he had not had problems with penetration. However, he made only a single comment about fellatio: "Oral sex has not been good."
That comment motivated me more than just about anything else could have, and I was determined to change his experience for the better. I have, but it has not been easy. I think you have to find a partner who really cares for you enough to go the extra mile and suck you with enthusiasm and precision. The precision was the biggest learning curve for me -- keeping my teeth off him was much, much more difficult than it had ever been with other guys.
Also, it sucks when you cant have sex for a couple days because she is sore or has a small tear.
This drives us crazy, too.
/\/\/\/\This! It seems that no matter how much lube we use or foreplay we do, my gf always gets worn out. I'm not overly thick but at 6.25" at the base it seems my dick creates enough friction at the opening to wear her out.
My husband is thickest at the base as well, and the entrance is where I get the most sore. Lube definitely helps, but like your gf, I still get worn out.
I do like the fact that on "pussy's day off" I can still stimulate him orally, or take him anally -- this is possible with a thick cock, even though the fear factor can be pretty significant at first. The key is to work in a little lube with one finger, then two, then three or more, gently massaging the anus while allowing it to relax and open. It can help if I massage my clit during this process as well. Then, make sure the anus itself is well-lubed, and also lube the cock before entering her gradually and slowly. If this is done correctly, the entry itself isn't that shocking, and movement is possible very soon thereafter. If it's done incorrectly, or too quickly, the entry feels like being ripped in half.
Making her too sore and having to take it easy for a day or two.
Again, I feel your pain. Literally.
Sometimes I wonder if my eyes have always been bigger than my vagina when it comes to wanting to be fucked by big cocks. But when I think about it, I don't think I could settle for less now that I know what it feels like. So I guess the associated difficulties just come with the territory; and when I get perspective about the whole thing, it's a small price to pay for the pleasure my husband's cock gives me.