I'd like to be proved wrong, but these issues are deal breakers for me, which probably means I won't get to work in the US, except on short secondments.
I also believe - but am not sure - that once you have a visa that lets you work in the US, any current tourist visa you have is cancelled, making staying there when you're between jobs is a major undertaking (at least in my case, I think it means a trip back home and to the consulates here to get the visa changed, so that may not matter all that much.)
If you switch between jobs, you can start working for your new employer as soon as you've sent off the paperwork- you don't have to wait for them to process it (which can take many, many months). However, you cannot have a gap between jobs- your employment must be continuous.