... but I read a lot about gambling and did my diplom thesis on online gambling.
This issue comes up again and again (and maybe offtopic in the online casinos forum, and maybe should be moved to another forum), especially when there's a dubiously large roulette win. I remember a story of some Serbian and Hungarian winners in London, see below...
http://news.bbc.co.uk/1/hi/england/london/3558273.stm
I'm from Hungary, and this story got high publicity in Hungary, and was heavily discussed on the Hungarian gambling forums I visit. My opinion is that noone can confirm 100% sure whether there's something behind, or this is just an urban legend.
However the opinion of some more experienced Hungarian roulette players and some dealers was that it might be possible for an experienced dealer to influence the result of the throw. Of course this is not something deterministic, but a correlation is possible. For instance a dealer might be able to throw one half of the wheel 30-40% more than it would be expected or one third of the wheel 20% more in the long run. A minority stated that it's even possible to try to aim at 6 numbers with a noticeable success. Of course nothing is assured, but they state that a significant colleration could be reached. I have to say that there was absolutely no consensus on the above statements. But you might now that Hungary is a country which provides a loooot of casino dealers all over the world (relatively good salary and easy-to-learn job abroad, many recruit offices, etc.), and I can reopen the discussion on the forum that they sometimes visit if you wish.
In the today's modern casino enviroment I don't think this is a real issue. You can hear stories about dealers who tries to "outthrow" you if you don't tip, or try to help you if you tip generously, or dealers who tries to throw in favor of the casino when one part of the table is full of chips, but it's almost impossible to tell whether these stories are true or not.