However, how is the maps performance on the 3GS? Does the vector-based graphics make it slower or faster? And is the lack of features noticeable? (arguably, it is a step back, afterall, some features are omitted, especially on the iPhone 4 and 3GS)
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Haha let us know

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In general, Safari should increase in speed between updates. However, yes, do try to use the phone (download apps, browse the web, multitask alot), and then evaluate the performance, and see if it can hold up like it used to. What I am primarily wary about it is the lack of ram on the device, which is a bottleneck to how the phone will perform while using it more intensively.
How are the new features on the 3gs Maps, offline reading icloud tabs and such.
I'll try my best!!
Offline reading lists Unavailable for the 3gs.
iCloud tabs
Works great. It has a 20sec delay or so, but since the intention is not to sync instantly but to be able to keep on reading or working a few minutes later while at the go, it does it job. iCloud tabs from a mac is displayed in the favorites in the 3gs, while in the mac there is a dedicated button.
Maps
Doesn't feel slow, but it does take some time rendering maps. Maps are completely functional all the time, problem is when zooming too fast you would get only a black screen for a few seconds, even over wifi, I guess over 3g it will be much slower. It works just as google maps used to. However it only has driving instructions. But overall it is much more responsive than google maps.
The included search engine is in the dull side. It could be considered even really awful. For example I live in Mexico, and when I search "Starbucks" it retrieves: Starbucks, Starbucks NV and a Starbucks in the middle of AUSTRALIA!!!! Seriously wtf??? When I choose starbucks it displays some of the closest ones. Nonetheless if I try to pull the search results again, it mixes my results with my favorited places and past searches (it pulled some really old queries from google maps) making a mess.
Camera
Pulling the camera from the lock screen is much faster and responsive than in 5.1.1. It's usable!!! In 5.1.1 if you were lucky after 20 seconds the camera would start, you would be able to take 1 or 2 pics and then a crash. That's not the case with ios 6, 3 seconds to open the camera app from lock screen (if it is already in the background). A huge improvement.
Music
I have itunes match. Using it in 5.1.1 was a headache... It still is. Bare in mind that I have a 50GB library. However music with match disabled works great, blazing fast. The new interface looks great.
Contacts
For some having facebook contacts, with photos and some additional information will be great. Unfortunately some FB users tend to use some wicked pseudonyms, rendering your contact list a mess. Duplicity is a major problem when syncing with FB. It get even worst if you also sync with your twitter contacts, in some cases I have 3 entries for the same person.
Passbook
It doesn't work. I don't know if it has to do with me being in Mexico, or with problems with the server, but whenever I try to pull the apps, it just says "unable to connect with the store"
Stores
They are fast enough. I mean, for being such a graphic intensive interfaces and the 3gs being as old as it is, it is amazing.
What features you should forget about for the 3gs:
Siri and everything related to it.
Dictation.
Location based reminders.
Maps turn by turn guiding
3D Maps images
FaceTime
Offline Reading Lists
Camera Panorama mode
Bottom line is: It is a solid release for the 3gs. I will go as far as saying that I don't remember it being as fast as it is under any other iOS since 4 (iOS 3 was blazing fast, but it had more to do with the inability to multitask than anything else). I didn't mention some other nice features because they are standard and have nothing to do with the 3gs performance. I tried my best to make it a performance perception review for the 3gs, rather than a generic iOS 6 review.