I can give you some info from the last two years that we dined there. In 2006we had a great server, but unfortunately I do not remember his name. He was really nice, and was great for getting our drink refills in a timely manner. Also, during this dinner we did not really feel too rushed. Overall, it was a great time.
In Feb of this year we had Patty (of course I remember the name of a bad server..lol.) She was not very nice, she was kind of abrupt and seemed like she would rather be anywhere else but there. We also felt VERY rushed, but I put an end to that. I just told the server who came with the next course to please slow it down a little bit, and they did. Patty, however was not very good with getting our refills. I remember I had to ask another server to remind her that we are waiting for our drinks for quite some time.
'Ohana used to be one of our favorites, but we are actually going to skip it in 2008 to try out different places.
If you go and they are rushing you, just let them know, and I am sure they will slow it down for you.
Also, as for requesting a specific server, that probably won't work since 'Ohana is very popular and it will probably increase your waiting time for getting a table.