Had the same deal with my wife!
wasn't interested, thought it was kids stuff, was happy for me to do it but had no interest in it herself!
Sat down to watch my new copy of Joe kid on a stingray last christmas eve, She sat and watched (I thought she'd be bored after 5 mins) and at the end she turned to me with a massive grin on her face and said "I want a BMX"
she came on the London charity ride last month and had a ball!
Out every chance we can get! she's picking up tricks really quickly and really really enjoys it!
If we had kids I know she'd be even more keen, for all the reasons mentioned above.
it's great for the kids to feel part of something too