to further ad from the previous post we arrive on aug. 21 at 9:00pm and leave for Addis on Aug. 28 at 6:00pm to pick up our adopted son. We would like to know if we have enough time to do a 3 day safari in masai and squeeze in Lamu? we have not booked a safari yet, we were thinking of shopping around the first day and hopefully heading off the next day, is that possible? also if we do fly to Lamu I presume we will have to be back in Nairobi the day before leaving to Addis, or can you depend on the flight schedules.

yes you can do a 3day safari to maasai mara and you will be expected to fly back to nairobi before addis

Save buying Masai bracelets and other jewelry for when you get to Masai Mara... a lot of ladies will bring stuff up to your car, haggle hard! It's a nice way to support the locals in this way rather than spending all your money in Nairobi.
In Narobi don't miss the Langata Giraffe Park and Carnivore restaurant. I suggest you come back 1 day early so that you can fit these into your itinerary... I'm not positive but I think there's a good craft market near the Langata Giraffe park.
I'd also pre-book a safari so that you can be guaranteed to leave right away...

You can perfectly squeeze Lamu provided you fly there (Kenya Airways and Air Kenya do fly there, the latter being cheaper and more convenient). Lamu is tiny so even in 2-3 days you'll get a good flavour of it. It is best to sleep in Shela than in Lamu town, as Shela is located on the beach.
I'd advise you to be cautious as to the flights. During low season, flights inside Kenya are often postponed of 24h due to not enough passengers aboard. During the high season (july-september) it is less likely to happen, so it's up to you. Be sure to book your flight in advance if you travel next to week-ends as the flights are full quickly - you can book on the Internet.
As for Nairobi, not so many things to do there. Langata giraffe center is indeed cute and you can feed the giraffes but it takes 20mn maximum. The David Sheldrick orphanage has 5 cute babies elephants and 500 shouting tourists between you and them. Karen Blixen House is beautiful but also visited in 20 mn.
There are quite a number of pleasant places to go out though. Talisman restaurant in Karen is a must for lunch. At night Osteria del Chianti and its nightclub Casablanca are quite pleasant, and Gipsy and Mercury are good places to have a drink. Carnivore is funny but the meat is overgrilled and it's packed almost exclusively with tourists, though its adjacent bar/nightclub has a more local/expat crowd.