I have interviewed and worked with several H1B's, and one thing that I have noticed is that while they're slightly cheaper, there is a cultural problem that is endemic. A lot of these folks are not able to innovate or thinking outside of the box. These are essential qualities in a good software developer (at least in my opinion). I have worked with one H1B whom is VERY good, and is able to think in addition to work.
I do believe that they are hard workers and that they try, I don't know how successful they will be in the long run. Most of the candidates I have interviewed have generally been hard-put to think through problems. For example, I would ask them how would they generally approach a problem (e.g. your users need to do x, tell me how you would do this). Most were stumped by this. I would even try to lob easy questions such as database normalization (You have a table that repeats the same fields like reference name 1, reference name 2, is this correct and if not why?).
There is also another problem, they aren't really that much cheaper ! The U.S. is an expensive place to live, and you can not really cut corners that much. We are talking about a difference of maybe 10-15k a year (at least in the ones I've spoken to). Most of the time, if you take the additional meetings that need to take place to re-review the requirements due to a little hiccup (see point about not being able to think though problems) and the costs could actually go UP. If you have to have an additional hour of meeting per week (very generous) with a PM, 3xDevelopers, BA (average if you have multiple dev streams). That's 52*5=260 hours. Average of $55/hour across all three roles, that is $14,300 for a single meeting hour long weekly meeting for the year. So the potential savings you got from one of the developers could be a wash. I have also noticed that non H1B programmers tend to work faster (again see point about working more independently).
So my point is that this maybe a situation of self correction. The trend might re-balance itself as more companies realize some of these realities; however, that would assume that the companies take such things into account instead of being penny wise and pound foolish.