Rebecca has some excellent points for you to consider. I would also check Craig's List and see what condos are renting for in Mission Bay. Then call some of the ads and see what the response is like. I would also ask the Developer or his staff as they would know of any units have been sold as rentals and what they anticipate market rate rents would be (at Arterra, Radiance or your building if it is not one of those.) You can also call Signature Properties and ask the staff at the King Street office what units are renting for at 235 & 255 Berry.
I believe renting will be very easy because of the new office construction in Mission Bay, the new UC campus and the proximity to the businesses in South Beach and the FInancial District.
Lastly, I suggest you take a real estate agent who does not work with the Developer to help protect your interests during negotiations including negotiating credits.
IMHO, with all the bio-tech stuff about to explode and the new university campus, Mission Bay should be a hot rental market. I would put a mock ad on Craigslist to test the waters as far as how much rent you might get and/or talk to some property management firms about managing the condo for you if you're not going to be here.
The last item to consider is that if you do an OMI (owner move-in) to move back into your condo, I don't think that you can rent it out again for three years so check with an attorney on this if you plan to come and go.
That said, yes, it is a great time to buy as SF prices keep going up. Just be sure to perform all of the due diligence that you possibly can beforehand.