I'm a woman, I cut both my own hair and my DH's hair. I use his normal trimmer/clippers that he uses to trim his beard, so it's smaller than a normal clippers. That's fine, it just takes a bit longer, but now I only have one clipper pulling double duty in my house instead of two. I cut it shorter on the sides and longer on top. It takes about 20 minutes but that's because I'm a perfectionist :) I take off the guard to clean up around his neck and ears (during which I'm glad for the smaller clippers). If you can buzz your hair and get 90% of the way there, if you can convince your wife to do the neck and ear cleanup I think that would be easiest. I like cutting my DH's hair, it's a time where we sit outside (in the summer) and chat. In the spring, I also like seeing all the bird nests in the neighborhood with tufts of his hair sticking out!
Only recently I got up the courage to cut my own hair. I looked up a bunch of youtube videos to get a feel for the technique (I have longer hair that has layers), then I did it on a friday so I could run to great clips and fix it if I needed to. Turned out fantastic, and I think it took even less time than cutting DH's hair :) I'm never getting a professional haircut again!
As for getting over the mental barrier, it was a no brainer for me cutting DH's hair. He has never in his life stepped foot in a salon and gotten a professional haircut. His mom used to shave his head once a year in the spring. I liked his hair shorter, but not THAT short (or that long once Jan/Feb rolled around! ha!), so I volunteered to trim his hair. My mom would always cut my dad and brother's hair, so I gave her a call and she talked me through the first time. Once I realized it wasn't so scary and I wouldn't accidentally gash his head open with the clippers, I got a lot more comfortable, and now I play around with length, style, etc to see what he (and I!) like best.
For the courage to cut my own hair, it was mostly out of frustration with professional haircuts. I used to go to an expensive place and get the whole shebang (shampoo, scalp massage, cut, style, etc) but I was never perfectly happy with how the cuts turned out. I'd also trimmed my own bangs for years, so I had gotten over that particular fear ages ago, but layers were still scary so I always wanted someone else to do them. I hated paying that much for something I didn't love, so I downgraded to super cuts, but same problem. So I decided, if I'm not going to LOVE my hair, I might as well have the hair cut for free :) I was only comfortable after I watched about 20 videos and really understood the technique and how it would turn out, but I'm very happy I did. Now I can trim my hair whenever I feel like it and make as many small tweaks as I want.