This is the same in all fields, and definitely has been the case in my 10 years doing music.
For the first 5 years I played in about a dozen bands, and it was a drag. One person with poor motivations can poison the well and make something that should be a blast into a complete bummer. Of all the musicians I played with in that time, none of them had officially released any music (and to my knowledge, none of them have released anything since then).
However in the last 5 years, I've had great collaborations over the internet with 2 musicians/bands I hugely admire. They had both released amazing work prior to our work together.
The way I see it is that actions speak louder than words, and the people before would always talk about how they "want to make the next X album" but may be just concerned with money, fame, chicks, or whatever. That's why they've never really done anything. However the two guys I've worked with recently had already proven that they know their stuff and have the passion and motivation, that they're in it because they love it, and that's why I've had so much fun working with them on music and we haven't had any arguments along the way.
I've released a lot of music in the last 10 years, all for free and on creative commons licenses, making no money and I'm not 'popular' by any means. But I think that's why they were also excited to work with me, because they knew I was in it for the same reasons they were (for the love of it, and for fun).
So I'd say if you're going to look into teaming up with people and your goal is passion as opposed to just money or popularity, check their previous work and see if it is up to the same standards you hold yourself to. Anybody can say this and that, but there are very few people out there who are really into what they do because they love it and want to do the absolute best they can.
And also working alone is a great thing; there's a lot less to worry about, and it's much much better working alone but being 100% excited and inspired than working on something that is a drag because of other people.