From Sh. @saad_alkhathlan, a scholar and specialist in moonsighting:

وردت أسئلة من بعض المسلمين المقيمن في بلاد غير إسلامية وأعلنت المراكز الإسلامية لديهم بأن بداية رمضان يوم السبت وأقول: كونوا معهم في الصوم وفي الإفطارفإن اجتماع المسلمين في بداية الصوم والفطر في البلد الواحد أمر مقصود شرعا لقول النبي صلى الله عليه وسلم ( الصوم يوم يصوم الناس والفطر يوم يفطر الناس.
“Many Muslims residing in non-Islamic lands have inquired about the Islamic Centers in their areas announcing the beginning of Ramadan to be Saturday. I say: Fast along with them and break your fast with them. Muslims being united in the beginning and end of fasting in one land is an objective of the Shariah, due to the Prophet’s (God grace him) statement “The fast is the day the people fast, and Fitr is the day the people break it.”

I would like to add some advice:

• - If you are a layperson, then please follow the advice above. Any mistakes in starting and stopping will fall on the shoulders of those in your locality that determined when to fast and when not to. You are no responsible to determine when the community should start fasting, but you are responsible not to cause dissent and trouble at a time best spent getting closer to Allah.
• - If you are an Imam, Scholar, students of knowledge, Shura member, Board member or public individual with influence please remember that even if you disagree with the decision made in your locality, please do not make your dissent public.
• Ibn Masoud disagreed privately with Uthman as to how to pray in Mina (2 or 4 Rakats). When the prayer came in, he prayed behind Uthman 4. Ibn Masoud’s confidantes said “Why did you disagree in private, only to follow him in public?” He replied “Dissent is evil” (الخلاف شرّ).
• - If you are someone tasked with determining when Ramadan starts, then remember that you have accepted an Amanah that even the heavens, earth, and mountains did not accept. Do what is best for your locality, the unity of the Muslims in it, and the image of Islam overall, while staying true to the principles of Islamic law and ethics. If you are not trained in Islamic law and ethics, then you should not be making this decision. Defer to those of knowledge if you do not know.

I am in Houston, TX this Ramadan, and so I will be starting and stopping my fast with the community here. Ramadan was announced to start Friday July 19th, 2012.
May Allah unite our hearts, rid them of malice, and fill them with the light of Allah’s speech this Ramadan. Ameen.