The information contained within still holds true, the guides to the likes of unlocking your bootloader, flashing using FlashTool etc are all still correct even with the release of newer firmware updates but I won't be adding anything further to it.
This thread is my personal attempt to provide Arc owners with a guide to getting the most out of the handset.
It draws upon the combined expertise of the Arc userbase here on XDA-devs and collates it in a simple, easy-to-follow format.
I am in no way claiming this as all my own work, full credit is given where due and my thanks go out to all of the wonderful, knowledgeable contributors whose work I am honoured to be able to showcase here.
Words of warning::
As with any modding or tweaking of a mobile phone, there is always a risk attached that you end up bricking, killing, blowing up, disintegrating, shrinking, beaming your handset to an alternate dimension or sending it forwards or backwards through time.
The risks are slight, countless people have undertaken the procedures listed in this thread with no problems at all - I myself have unlocked the bootloader on my Arc, rooted it using Bin4ry's image-flashing method, deleted some of the pre-loaded apps, flashed the 2.3.3 update using FlashTool are re-rooted again using Bin4ry's method... and my Arc is absolutely fine.
However, if you somehow manage to mess up or break your phone in any way, neither myself nor the authors of any other threads or resources I link to accept any responsibility or blame for what happens.
No-one is forcing you to do any of this, it's your own decision. If you're uneasy or nervous, just don't do it.
Also, whilst unlocking the bootloader is supported to a degree by Sony Ericsson, rooting, flashing custom ROMs, all the rest of it is not and there is always a chance you'll end up voiding you warranty.
As above, no-one else accepts any responsibility for your decisions and actions.
Also, on a personal note, please don't PM me asking for help.
I don't wish to sound rude or ungrateful but I'm not a developer, I'm not coming up with new tweaks/mods/ROMs or anything like that, everything I know is laid out in this guide in a manner that should be plain and simple to follow, if there's something that isn't covered here chances are I don't know either.
There is a whole section here for the Arc literally teeming with people happy and willing to answer any/all questions you might have, so you'd probably find your question answered quicker that way than if you were to contact and individual and ask for help.