I agree with most of what's been said before. At our club we have many male and female fighters and we all train hard together - there is no easier option. Our coach is great and doesn't differentiate between us in any way at all, I think his attitude is reflected throughout the club.
When sparring the only thing that really matters is size ( and experience but obviously mixing differing levels of experience is how we all learn), I stay away from some of our biggest guys simply because they're HUGE compared to me and realistically I'm never going to be up against someone who's 50 odd kilos heavier than me-although on the odd occasion I've had no other option but to batter in there.
I've spoken to some guys about this in the past, notably guys who are new to sparring. I've encouraged them to attempt to hit me, as that's the point of sparring, some have explained that they don't feel comfortable doing this. This isn't my problem though it's theirs so I continue to spar as normal and often they do pick it up a bit more.
I enjoy sparring with both men and women and there are as many differences within each of these groups (as regards style and approach to sparring) as there are between them.
At the end of the day noone should be treated any differently on the grounds of gender and anyone who steps into the ring commands the upmost respect.