There are several aspects of this, depending on the definition of "conservative", and depending on where you apply the label to the church: its doctrine, its leaders, or its members.
This is where the Catholic Church is liberal: if you look at self-identified Catholics and how they vote, you see a 50-50 split beween the GOP and the Dems. It used to be worse, as the Catholic blue collar ethnics were solidly Democrat when the Democrat party was about labor issues and poverty relief.
That might be traced doctrinally to the Catholic doctrine of necessity of works of caritas, love, -- which all too often is mixed up with government charity programs in people's minds.
However if you look at the picture today and take into account not merely self-identification as Catholic, but also frequency of church going, you see that the more devout the Catholic people are, the more conservative they are politically, and the trend is good, too. Church-going Catholics are, for example, largely credited as the group that shifted the balance for the GOP in 2004, despite the nominal Catholicity of Kerry.
Let us turn to doctrinal matters. Here we have a very mixed picture. The Catholic doctrine is extremely conservative in terms of cultural policy: it is uncompromising on contraception, abortion, euthanasia, re-marriage, and gender specificity and complementarity. It is not particularly conservative in economic policy as it sees unfettered capitalism problematic as much as socialism. It is also opposed to death penalty, although not in the same way as it is opposed to abortion. The former is seen as in need of careful justification but permissible in some theoretical circumstances, while abortion is seen as an absolute intrinsic evil. It is very nearly silent (dogmatically speaking) on evolution, where the Catholic dogma leaves a wide berth for nontraditional opinions.
The entire doctrinal edifice of Catholicism is not subject to change, democratically or from Rome (it is subject to refinement, as, for example, the whole set of "life" issues was a refinement of doctrine in response to modern challenges). The Church simply cannot change her mind on, for example, contraception, like the Protestant communities did. So, if you definition of conservatism is resistance to change, then the Church is extremely conservative. It is quite simply a Medieval institution that will stay Medieval till Kingdom come.
Thirdly, we have in the West the laity that pretty much spans the political spectrum, and we have bishops that are a reflection of the same fairly liberal culture, caught between the conservative dogma and the relatively liberal laity. We also have the lavender mafia, which awaits its Inquisition. Like I said, it helps to identify the devout conservative undercurrent not reflected by the statistics. There are some embarassingly liberal parishes, and some rigidly conservative ones. One thing you need to bear in mind: while the doctrinal teaching pretty much defines Protestant denominations, it is participation in the sacraments that defines Catholicity. Where a Protestant denomination splits over doctrine, the Catholic Church expects her members to know the doctrine, struggle to embrace it, repent of the failures, and persevere, but it would never turn a Catholic away. Well, nearly ever: it takes a scandalous public apostacy to be publicly ex-communicated. The Catholic Church is, in other words, catholic: for everyone. So she will never become, as a body of members, far from the nation as a whole. This incidentally, explains the lack of fire and brimstone preaching, as a priest is always careful not to alienate the sinner and push him into apostacy.
Lastly, the Church sees historical time differently than, for example, a Jew does. Our history is not linear from Creation to infinity, but rather it has a center at the Cross, with prior history leading to it and present history looking back to it. This means that on the deepest level what we conserve is the Cross, and not, for example, the Judaism of the Prophets that predated it.
Quite true. And well put.
You offer another interesting idea, that Catholics are defined more by their communion with the Church rather than with their doctrinal beliefs. This is similar to Judaism's definition of a Jew as the son of a Jewish mother rather than someone who believes a certain set of doctrines. Perhaps it is my own Bible-Belt upbringing, but I always thought that beliefs were pretty darn important and that a political unity in the place of doctrinal unity is a will-o'-the-wisp. However, I note that there are rightwing Catholics who insist that it is Catholicism that demands doctrinal correctness while Fundamentalist Protestantism is an emotional experience.
As to a lack of "fire and brimstone" preaching, I would advise that you should appeal to the culture you hope to reach (granted, no one really wants to reach Fundamentalist Protestants--white ones, at least--since they provide a convenient scapegoat to make all other religions look respectable to secularists). I might also suggest that Catholics don't want to hear about Hell because they can still go there. Calvinists can listen to sermons about Hell all day, since (in the words of Baptist preacher Charles Stanley) they "couldn't go there if they wanted to." But this raises an interesting question: isn't it the people who are in danger of going who should be hearing about it? And why do Calvinists have such an interest in the subject since they are "eternally secure" from ever going there?