Rav Chanina said to Rav Ashi that the people of Bavel who are north of eretz yisroel (i assume it means more north than east but really north east), should daven to the south. This is based on the premise that the direction of tefillah should be toward eretz yisroel. Tosafos 25a explains that this opinion is consistent with the braisa in brachos 30a that says that one should face toward yerushalaim. However, in the gemara 25a, Rav sheisheis told his assistant that he should allow him to daven in any direction except toward east. Any direction is technically find because he followed the opinions that the shechina is in all directions, even in the east, but since idolaters pray toward the east (because they worshipped the sun that rises in the east), he made a special effort not to daven in that direction.
Most Jews out of eretz yisroel live west of eretz yisroel (some of us further west than others). Based on the first approach of davening toward eretz yisroel and yerushalaim, we should be facing east (or perhaps whichever direction would be the quickest line drawn to eretz yisroel, which in california would be more north than east - but that is not the minhag). But, based on the concern of idol worshipers we should refrain from davening to the east, as rav sheishes was careful not to do. R' Moshe (dibros, heara 44) explains that in the time of rav sheishes there were many idol worshipers who would pray to the east. Therefore, even those who live west of yerushalayim and should be praying to the east, would not. But nowadays we daven to the east because we are west of E.Y. and there no longer exists idol worshipers who pray in that direction.
Being that there are now a large # of muslims (yms"m) who live west of mecca and therefore pray to the east, perhaps we should reconsider the sensitivity of rav sheishes and no longer daven to the east???