It depends really what you mean by doubts about Judaism. In terms of doubting what Judaism teaches about God, then I probably doubt it as often as I believe it. I don't think that any rational argument could ever completely convince me to believe in God, because if the statements Judaism makes about God are true, then rational argument is less than relevant. So the only time I'm without doubt is when I experience God's presence personally. But in hindsight I can always doubt those experiences too; perhaps it was just a construct of my mind or I was victim of some form of suggestion. Equally, it's very rare for me to be 100% atheist; I'm usually aware that theistic Judaism might have some fragment of the truth.
It's never struck me as a big deal, really. Judaism has always felt to me like a very relaxed environment towards belief or unbelief and anything in between. (I should add that this is not the experience of all my Jewish friends.) Nobody's telling me what I need to think in order to fit into the community. Belief most often isn't talked about, and when it is discussed, it's generally accepted that some people have more sense of the Divine than others and people read texts and liturgy in more or less literal ways depending on their inclination.
There was a time in my life when I had serious doubts about everything. Whether there is any sort of meaning to be attained (I never really believe that existence has intrinsic meaning), whether it's even worth bothering trying to behave morally rather than otherwise. I was still Jewish when I was in this situation though; I tended to express my anger at reality as anger at God, for the most part, and it was a Jewish moral framework that I was thinking of rejecting. I overcame this sort of doubt because I simply couldn't continue to exist in a state of such moral despair; it was a deliberate choice that whether or not I had good reason to believe it, I was going to live my life as if there was a point.
It's hard for me to doubt whether I should be Jewish, in some ways. It's a major part of my identity and has thoroughly influenced the way I think about most things. I don't think I could stop being Jewish any more than I could stop being female (even if I were to change these things, I would still have twenty-five years of experience of living with my current identity which I couldn't just ignore).
Doubts about whether I should live Jewishly in the sense of keeping religious customs, being part of the Jewish community and so on, I can certainly imagine experiencing, but I can't say I ever really have. The exact level of my practice is something that's continually under examination; for me, that's part of the point of being Reform. But on the whole my practice has tended to get more extensive over time rather than less, I've taken on new observances that I didn't previously keep. But that doesn't mean that the trend will always continue in that direction. I do doubt whether some of it really matters very much; I think it's possible to invest too much in avoiding eating certain foods and that kind of thing. But that sort of doubt doesn't really lead me away from Judaism, it just causes me to lean more towards the Liberal / Progressive end of the spectrum where there tends to be much less emphasis on ritual.
I sometimes doubt Judaism as an institution, particularly when there's stupid communal bickering going on. Like a few years ago, a rabbi in a leadership and spokesman position within Orthodox Judaism publicly refused to attend the funeral of a Reform rabbi who had been extremely well-loved and influential throughout the Jewish and wider community. And privately justified this decision by calling the Reform rabbi an "enemy of Judaism"; the rest of the community learnt of this because someone saw fit to leak his private letter to the Jewish Chronicle. Everybody concerned behaved incredibly badly; the rabbi who refused to attend a colleague's funeral for political reasons, yes, but also the section of the Orthodox community that put pressure on him to take this position, and the journalists and editors who thought that stirring up hatred and sectarianism would sell newspapers, and the people from the Reform community who went around for months saying that obviously Orthodox Jews are all stupid bigots because look what [this senior Orthodox rabbi] said. I came quite close to dropping out of Jewish life because I was so sickened by all this stuff. I overcame that by coming to the conclusion that if all the decent-thinking Jews took that kind of decision, then the bigots and petty, power-hungry fuckwits would have won.
It seems to me that Judaism is the best framework for me to be the person I want to be. That's not an absolute; I can imagine changing my view on this point at some time, but so far I haven't. I don't really have any view about whether Judaism is in some absolute sense the best religion / philosophical construct / moral system etc; I'm not sure that kind of question is meaningful.
That was really thought-provoking, thank you shreena. Does anyone else have any questions for me?