ICS arrived this morning on my htc Sensation. It is currently installing.

Around 296MB (thank goodness for data flat rates), the download finished in about 20 minutes and the update has taken about another 15 minutes so far and has just finished.

So, up and running. Very nice, feels a bit quicker and it looks very smart. Sense is feels a lot less intrusive, they seem to have mixed Sense into the "native" ICS look and feel.

Very nice so far.

The face unlock is a bit hit and miss - I sit in an office with a window behind me, which the camera doesn't seem to be able to cope with, the brightness from the light outside is too high, leading to bad contrast (washes out the outline of my head, whilst leaving my face pretty much black). When I rotate to have a more neutral background, it works fine.

The new busy animation is very nice.

The whole thing looks very smooth and modern. I like it a lot.

Can't talk about stability yet, it has only been on the phone a couple of hours. If it is anything like the previous version, then the phone will probably go months between power cycles.

It got pushed to my Nexus S overnight, so I was pretty pleased to wake up and find ICS 4.0.4 goodness waiting for me to install (took only couple of minutes).
I have to agree that it feels quicker, that was my big concern as my droid is only single core. But it feel even faster than 2.3.6 Gingerbread. Also it somehow made my screen/phone look bigger, it feels like a new phone now. I haven't found anything or any app that isn't working now so it's all good.

One thing I am not impressed with is that it was pushed and downloaded without my approval. Only 140mb (vanilla OS without a skin) but could have been costly should it be later into to the month as I am on 500mb tarrif and anything abouve that is charged per MB.

I thought Android had options to update over wifi only?

It does.

Mine told me that the update was ready, but as I wasn't on a WLAN, it wouldn't download without me going in and overriding it. I put the company SIM card in, as I don't use that for data anyway and it has a 5GB limit (private has 2GB limit).

I think you mean update of the apps in Google Play where there is indeed an option for this.
However I don't have an option available when it comes to system updates.

It should be there, it certainly is on the htc Gingerbread.

I have no idea where I would set the OS updates to happen only over WiFi. I do have the normal updates set for that, but it specifically states "apps".

Is it being pushed by the network provider? If so, it shouldn't count against your usage!

You can't. But, at least on mine, it says that the update is over 20MB and you have to explicitly tell it that it is okay to download over 3G.

Mine was pushed by htc directly (unbranded phone), branded phones will be pushed by the provider, so I think you are right, it shouldn't count against your data volume.

My system updates ask me if I want to download over any connection or wifi only.