You also have to copy over/match the "extensions" section of your Preferences file that is stored in Local Settings\Application Data\Google\Chrome\User Data\Default or Chromium\User Data\Default as may be the case. (Or the corresponding directory for Vista and Win7 users.)

I have always just copied the entire User Data folder (first deleting the one on the "target" computer.) And if I remember to do so I clear the cache before copying just to cut down on the size.

That seems to work perfectly for me on a Dev to Dev copy. I have never tried a Dev to Beta or Dev to Stable. In my case my source is usually an XP machine; the target is Win7 although I have reversed that; it does not seem to make any difference.

Yes, copying the entire User Data folder will most definitely work; that's just making a copy of your entire browsing profile. I guess we are just trying to nail down what specific details constitute Extensions only.

And of course, it's probably a good idea to clear the cache before copying your User Data, unless you always want to copy around 1 GB or more worth of stuff.

In theory, this method is guaranteed to work as long as you stay within a major version. That is for now, you can copy between different Chrome 4 Devs and also between Chrome 4 Dev and 4 Beta. There is no guarantee or provision that any Chrome data storage is compatible between major versions, eg. between Chrome 3 and Chrome 4. And of course, this works between Windows versions because so far, there is only one version of Chrome for all Windows versions.

There was some developer talk about this issue for Chrome between platforms (ie. between Windows/Mac/Linux/Chrome OS/etc.) I saw it a long while ago and might have to search pretty hard to find it again. If I recall, I think the devs were leaning towards not guaranteeing compatibility between platforms.

for syncing extensions to a portable version of Chrome, I copied the contents of the Extensions and Local Storage folders, the Preferences file and the extensions show up in the portable version of Chrome;

Having spent some time testing this out using ChromePlus , which is at the same version as the Dev channel (almost) ...

I found the following ...

The Preferences file is needed to load the extensions and the Local Storage is used for the extensions customisation and it also loads the icons above the bookmarks bar ...

In actual fact if you look at where the extension icons should be you will find that they are actually there but not displayed ...

If you 'mouse' over where the extension icon should be you can actually ‘click’ on the icon ...

However the extension won’t function because it is missimg the info that is in the Local Storage folder ...

So basically you need all three elements to make your extensions work ...

Btw (if you didn't already know) the Preferences file also contains info on things like your Theme, Homepage, Country ID, Syncing and a couple of other things ...

Thank you all...
I have a lot of testing to do now...
It is a pity that Google does not provide Extension sync like they do bookmark sync
as Mozilla does: https://mozillalabs.com/weave/

I'm sure there'd be a solution in the (near) future. Extension are just (officially) presented, so be patient

patience is not my best ability

Mozilla was announcing Weave even before the very existence of Chrome...

http://stefanobordoni.interfree.it/S.../horodruin.htm

This program allows you to synchronize more than 2 folders with just few clicks. It's very simple, but you first must read the included documentation.

I think I might need this

What I finally did is to take a conservative fairly manual road:
On my main computer I bookmarked all the extensions I have installed. Mainly from 2 sources:
https://chrome.google.com/extensions & http://www.chromeextensions.org
On the laptop it is then fairly simple to adjust manually my extensions...
One advantage is to have all the info about the extensions in one place...