I have one and have quite enjoyed it! It works very well, but make sure you get a WeVibe II (the newer model) if you get one. It has more settings than the original, and gets better reviews.
The WeVibe can indeed be worn during sex, and it's fun. It is especially nice for doggie positions since it provides enough stimulation for a lady who relies on clitoral stimulation to cum. It can also be fun for anal (for similar reasons). I cannot speak from the male perspective, but I believe that my partner enjoys the vibrations. He also enjoys the fact that I sometimes have huge orgasms wearing it, and in positions where I cannot cum easily otherwise. That gives him some new sensations, too. It is a fun addition to the repertoire of things we can do together.
As for becoming reliant on vibration and toys in the bedroom -- I can speak from experience here, and I would say that is a fallacy. Toys like vibrators are fun, but they are just an add-on in a good relationship. I cannot see becoming reliant on them unless my partner got them out ever time we were together. Like many other good things in life, sex toys are great -- but in moderation.
When we reached the point of introducing sex toys in the bedroom, we went through a phase of trying out lots of them. Some work much better than others, and there are so many on the market now that it is easy to find lots that look like fun to try. We have a whole bag full. In truth, however, we have used them less and less as time has passed. After the novelty wears off, many are just not worth the effort. More often than not we don't use toys at all. But when I think about it, the WeVibe is definitely one of the ones I would keep if we decided to clean house and get rid of the toys we don't have interest in anymore. It's a keeper.