[HTC Desire S] anchemis:
Hi Sky770! Welcome to Android! (and XDA!) :)

First of all, you need to understand that ROOTING and S-OFF are completely different things.

ROOTING -> is where you allow apps to access certain protected parts of android (just like UAC in windows 7). A few apps won't work without rooting (TiBackup for example). It is typically done by some software exploit which will install the SuperUser app on your phone (that allows you to 'allow' or 'deny' apps that request superuser permissions, like UAC).

Rooting can be done quick and painlessly using SuperOneClick or GingerBreak (whichever suits your fancy!) It shouldn't affect your warranty, as technically you should be able to 'unroot' it relatively easily using the same software solutions.

S-OFFing (aka Bootloader Unlocking) -> is where you hack the bootloader of the phone to allow you to mess around with 'protected partitions' on your phone.

A stock phone from HTC will have its bootloader locked (aka S-ON), which means you cannot install non-HTC sanctioned ROMs as the /system partition is protected from non-HTC authorised changes. On the other hand, a phone that has its bootloader unlocked (S-OFF'd) doesn't have this protection, so you can install pretty much anything you want on it.

Various tools exist to S-OFF a stock Desire S, but most users typically use one of the 3 methods:

1. XTC clip (hardware method): most verstaile, but obviously you need to buy (or borrow) someone's hardware to unlock it

2. Revolutionary (software): pretty straight forward provided you know how to follow instructions using adb tools. Revolutionary will ONLY work if you have a bootloader (hboot) version of v0.68.xxxx (although methods exist for you to downgrade higher versions of hboot)

3. HTC Dev Unlock (software): this is where you contact HTC servers with phone identifying data, and they give you an unlock authentication.

With HTC Dev Unlock, as you've sent your phone ID to HTC, they can theoretically say you're warranty is now void as you've been messing with the bootloader / ROM etc. For Revolutionary, methods exist for you to 'relock' your phone so in theory HTC will never find out what you've done (in case you need warranty repairs etc.)

It pretty much boils down to personal taste. A lot of people swear by the Sense interface, though most common complaint about Sense 3.0 is the memory/resource hogging / slowness (despite the Desire S being a pretty fast phone).

Again, you can root without having to S-OFF, depends what you want to do.

If you just want to use software that requires root, then just root.

If you want to flash custom roms onto your phone, then S-OFF.

See above. :)

See above. :)

Yes, in fact you can install ANY ROM after S-OFF and rooted.

OTAs are a bit tricky... there is a setting in the phone called CID, which your carrier controls what firmware updates you can receive. Carrier-branded OTAs are typically released later (if at all...) due to the various amount of modification / theming / bloatware installed (*cough cough* Orange...)

The CID setting will determine whether you install non-branded (generic) firmware or carrier-specific firmware. There is currently no way to change the CID except using XTC clip.

S-OFF

Go to BOOTLOADER mode (vol- and power) and find out what version of HBoot / Phone Software you have on your phone.

If it's v0.98.xxxx then S-OFF is easy, just use Revolutionary.

If it's v2.00.xxxx then you need to downgrade first before using Revolutionary. (The downgrade process is a bit complex, though generally involving downloading a region/carrier specific OLDER firmware for your phone, please read the forums and follow the instructions!)

(Optional step) After you've S-OFF'd with Revolutionary, your hboot should be v6.98.1000. (The catch is that you can't RUU restore the phone with this version of hboot, say if you want to return phone for warranty repair).

To counter this, most people overflash this with an engineering bootloader ENG v0.98.xxxx. Again, read the forums about this and RUUs.

ROOTING

Use either GingerBreak or SuperOneClick down to personal preference.

I use SuperOneClick, as you basically plug phone to computer, enable USB debugging mode, and click Root... then wait for it to be done!

Hope this helps! Happy Androiding! :)

---------- Post added at 02:03 AM ---------- Previous post was at 01:49 AM ----------

Just my (personal) opinions, so please no wars...

Sense 2.1 (gingerbread, HTC v1.x roms): the retro- (HTC desire) look, pretty snappy with less (but still some) HTC bloatware

Sense 3.0 (gingerbread, HTC v2.x roms): more eye candy (sensation-like) look, memory-hog and full of HTC bloatware

AOSP Gingerbread (CM7): nexus s-like look, very snappy, NO bloatware (but some newer phones have camera issues

Sense 3.6 (ICS, releasing q2/q3 2012?): no idea why HTC bothered to release 2 versions of ICS, this is clearly the inferior version (see Sense 4.0 below).

Sense 4.0 (ICS, ported from One series, unlikely to get official Desire S release): eye candy (One-like), snappy, less (but still some) HTC bloatware, still some issues at the moment, but hoepfully these will get ironed out soon.

AOSP ICS (CM9, AOKP etc.): galaxy nexus-like look, very snappy, NO bloatware, currently have camera issues (but people are working on this)

OTAs are usually full of carrier-branding / bloatware, generally generic non-carrier branded ROMs are cleaner and faster. However, HTC and carriers tend to be quite slow in releasing ROMs (it makes more business sense to tempt you to buy a new phone than get free new software).

This is where custom ROMs excel, as many great devs (ie. proxuser) will port the newest version onto the Desire S... which will give your phone a new lease of life once HTC / carriers abandon it...