Here's my rationale on things:
1. A video rental usually costs a few bucks. I'm pretty sure it's about $2 around here (I should know, I just rented one tonight). Meanwhile, it's like $9 at the theater. If you want to buy the movie and watch it over and over for eternity (aka buy the video) it's usually $15-20, or roughly two movie tickets. I only buy a movie if I've seen it and really like it. Sometimes that initial screening will come on a rental.
2. The cost of refreshments. My favorite technique for going to the theater happened a few years ago when McDonald's sold 44 oz drinks. In the summer of 2002, they had these exchange students working there. One was a really cute German girl and she would always give me a 44 oz water for free instead of making me pay for the cup (most places give you a child cup if you ask for water). I'd take that and only buy the popcorn. Well, then the popcorn price went up, the girl left for Germany, and I switched to chewing gum. One piece usually gets me through the average movie, I bring two if it's a long one. If they're bought in bulk (multipack) they're like three cents a stick. But seriously, you can spend more on refreshments than a ticket.
3. Comfort factor. The theater in my area was built in 1978 or so. It also looks and feels like something built in 1978, wear and tear included. The seats are ripped, the floors are sticky--the area's not run down at all, you'd think there would be a better theater. The screens aren't that good either, and I have two choices--sit in the back and not be able to see that well because the screen's blurry from age or sit in the front and strain my neck to see the movie. At home, I have my easy chair and a 24" Sony Wega. It's a CRT TV, only two years old, and is sharper than the movie screen. Brighter, too.
4. The one aspect where a theater may get a nod is when you're meeting a bunch of people. My place isn't the best for watching a movie. I really designed it for one person to watch TV, but have enough chairs sitting around that people can pull them up, or just sit on the floor--that makes eight chairs, my easy chair, and also my ottoman. Of those eight chairs, only one has a padded back. None of them rock, and most are folding chairs. The most I've had over since I got this place in December is four and we all sat on the floor to watch a football game.
5. Now if it's one other person, like if I want to have a romantic evening with a lady, the place could possibly work out. The easy chair is big enough to fit two very snugly. Also, at least for me, I like to keep affection mostly in private, so I wouldn't have to worry about anyone staring at me if I kissed her or something.
6. My dog can sit around with me at home. No go at the theater. That right there makes home the superior choice.