Many Olim have difficulties finding jobs because they don't speak good Hebrew, and because, unlike people who've been living in Israel for many years, they have not been able to build the informal networks that help finding a good job.
Many Olim have also difficulties getting used to the level of salaries, which is lower than in the USA. Some travel back to the US because they know they can get a job paid twice as much as in Israel.
The problem I've often seen is that some Americans travel to Tel Aviv on holidays and enjoy their time there because they can afford to enjoy this great city on their US salaries. Some of them don't realize that once living in Israel on an Israeli salary, they may not been able to afford living in Tel Aviv and will end up living in Modiin or Beer Sheba, which are usually less popular with US or European Olim. It happened to two friends of mine; one of them left Israel, the other decided to stay.
That's why it's so important to travel first to Israel and discuss with Olim with more or less the same profile as you. They can tell you what to expect, so you can make an informed decision.