Ok, thinking a bit more about "Weave" and what bothers me about it.
So, "Weave" is an attempt to provide off-site storage for basic Mozilla-y stuff like preferences, history, passwords, and other bits that one generally also finds in the Privacy "Clear This Upon Exiting" settings. (Frankly, that should be your first warning.) That data is stored within a somewhat nebulously defined "Your Firefox" cloud which is a set of servers provided by Mozilla.
While i'm quite sure that there's proper levels of encryption and protection to ensure that only YOU are able to get this centralized, incredible wealth of information that any phisher would give their sexual organs to get ahold of, it's being billed as "extensible" meaning that it's going to become the prime vector of attack for trojans people install onto their machine.
Plus, there's the "social" aspect of it that also feels pretty tacked on. (In one of the use cases, you've got folks collaborating on bookmarks.) Again, it's my hope that this is fairly tightly controlled among known parties and doesn't become a potential vector for spam. Before you too quickly dismiss that idea, let me say that i'm regularly approached by folks that want to set up networks of group bookmarks where said bookmarks are pushed down to the group members. Not just "queued for review" like the del.icio.us "for:" tag, but actually inserted with priority into user's active marks. Why not, really? It's a great idea to keep folks up-to-date, and services like StumbleUpon, Digg, and Reddit pretty much provide that capability with live bookmarks.
My problem is that unless the user is willing to go through steps to set that up, you're introducing the ability for bad guys to do bad things. i can easily see how this sort of feature could be horribly abused much the same way that email, IM, and a host of other social services regularly are. (Jabber comes pretty close to solving this problem by again, making the conversation request an element of mutual consent, but that's not really setting the world on fire.)
The problem i have with Weave, (as well as a great number of other syncing solutions), is that they don't really solve the problems i have. My bookmarks are different between home, work, and mobile because the contexts i use them are different. Likewise, i'm kinda happy that my passwords, cookies and other identifying elements aren't publicly available or downloadable (even for myself). It is eminently trivial for me to make these data sets available via highly secure links on demand. Frankly, i want parts of my life to be less accessible and require some thought or action to manage.
Granted, i know some folks are happy to surrender great heaping wads of personal information to advertising companies. i don't happen to be one of those, but hey, i'm abnormal. i like to think that the only person who has an inordinate interest in what i'm doing should be me.
i still stand by my previous points, though, and until my rampant paranoia is sated, i'm going to pass on this.
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That plugin is simply evil.
I dislike google's antiphish thingy in firefox (and routinely disable it), I dislike various "add your RSS feeds to this here nifty service" which serves me bloody cookies from those bloody servers when I access the bloody firefox OPTION page (bloody cheek!) …
thanks for the thumbs-down on weave, I'll steer way clear of it.