Hi Guys,
I did this trip in Sep/Oct 11, I was told my my Local Nurse that Yellow Fever for where you are going is optional, its totally up to you, I didn't have it and there were no problems, malaria tablets are a must.
To clear a few things up about the dolphin safari,You don't get to book your trips until you arrive at the hotel in mombassa after the safari part, so you have until sunday to think about what you are going to do. I did this and had a great time, you leave the hotel around 6am, its about a 2-2.5 hour drive to the boat, the last 15km is down a dirt track, you then get onto the boat, have breakfast and then spend the next few hours searching for dolphins, once you have seen the dolphins and had lunch the boat then goes to a reserve where you do some snorkling, I was lucky enough to swim with some green sea turtles (wear a t shirt when swimming), you get off the boat around 4pm and head back to the hotel, its a long day. 6 of our group went on the trip 3 of us had a great time the other 3 hated it (it was the travelling).
I would say if you want to see dolphins and possible swim with sea turtles then go for it. I would also suggest you do the 1/2 day mombassa trip, get your wooden figuers when you visit the co-operative, don't buy from hotel shops or beach traders or the masi warriors who put on a show in the hotel one evening, the co-operative sells the figures at 4 times less than everyone else.
Have a great trip
Martin