I followed a guide on this forum,
How to debrand an HTC Desire and update to Froyo - Broadband Genie
Like some of the people of this thread, I was hesitant to do it fearing I would brick my phone. In reality it took about 10 minutes to do (most of that was downloading the generic rom (link to that on the above link).
Not only did this get rid of the orange rubbish (though I would recommend not having your sim card in the phone, backup the entire contents of your SD card and having a backup of your contacts - I use WaveSecure from the app store), it also gave me access to Android 2.2 through the OTA updates from HTC direct (previously I was running 1.15 thanks to Orange, so the 2.2 update was not happening).
The removal of the orange crap gave me a fully working phone, access to the updates for it straight away, and left me a happy person.
I have been a customer of orange for the last 10 years or so, and have always had a problem with them putting their own stamp on phone firmware - now that I know Android phones can be made generic, then I will do this with all future phones.
I appreciate why orange do their own branding (to make us spend money on their app store, spend money using their navigation etc) but there seems to be a simple way round it. It is annoying, and I agree that I should not have to go through the hassle of debranding a phone from orange, but what the hell - it seems to be a simple process, I lost no data, and my contract from Orange is the best I could get compared to other networks (I refuse to have an 18 month minimum term).
Sorry if this rambles a bit, not had my coffee this morning