[Android Software/Hacking General [Developers Only]] idasein:
Solution for goapk.com (or just rooting branded phones)

Ok, I've managed to solve the issue based on the information from this forum, so here's the solution (which is unfortunately quite long, but it works... at your own risk, of course):

The issue: A bought-in-China HTC Desire, branded by the horrible goapk.com with no Android market access. Could only access some Chinese market called GoMarket created by goapk.com. This could also apply to anyone with a branded phone (eg. branded by a carrier) that could not be rooted with UnrEVOked3.

Solution: Downgrade the OS to an unbranded HTC Sense Android 2.1 with a goldcard inserted in the phone. This makes it possible to root the phone using Unrevoked and then you can install any of the Android ROMs you like on it. Technically you could stop after downgrading to Android 2.1 and not bother rooting (since you'll already have Android Market access by then), but you'll probably want to continue so you can finish with Android 2.2 on your phone.

Method:

Step 1:

Get an extra MicroSD card (2gig or whatever) and create a goldcard. You need this because your phone is branded with goapk.com and this is part of getting rid of that. Find out how here: android.modaco.com/content/general-discussion/305672/creating-a-goldcard/#entry1233023

Tip: you don't need an microSD card reader. You can format the microSD card in your phone by connecting your phone as a USB drive, and right-clicking the drive and formating. It MUST be FAT32 format, NOT FAT, so do it from the computer controls, not on the phone itself (because the phone itself does it in FAT format)

Step 2:

With your goldcard in your phone, you can now downgrade to Android 2.1. This kills two birds with one stone. A. It removes the horrible goapk.com branding and B. Lowers your hboot from 0.93 to 0.83 which makes it possible to root your phone. Instructions here:

xdaforums.com/showthread.php?t=768256

Tip: if it fails the first time (as mine did) and it can't find the zip file at the end, make sure your goldcard was FAT32.

Now your phone will be running HTC Sense 2.1 unbranded, with access to Android Market. The next two steps will allow you to put any of the Froyo versions (with Sense or without, your choice) on your phone.

Step 3:

Root your phone with UnrEVOked. Instructions here:

rootmydroid.co.uk/guides/general/howto-root-your-htc-desire-wildfire-evo-incredible-with-unrevoked/

Tip: His instructions are great. His download pages are horrible, but they work eventually, just keep clicking.

Step 4:

Install any of the custom Android ROMs available. Instructions are also found on the above link for rooting the phone.

You can choose from any of the ROMs listed here: xdaforums.com/showthread.php?t=809328

I went with DeFroST, which is a nice Android ROM without Sense, since Android is better off on it's own, IMO.

Tip: If you don't have an MicroSD card reader, make sure you put the ROM's zip file on your MicroSD before you wipe your phone (Pt. 3, point 4 in the guide).

That's it! When you finish, you'll have rooted phone with full Android Market Access and any version of Android you want on it. Sorry I couldn't recommend an easier way. Now if I could just get my hands on this damn person at HTC who let goapk.com crap all over this phone to begin with (or Google for not putting any rules in place)...