I havnt really encountered any or heard about any major ones.
The bootloader is locked, which means you cant install custom kernels and such. However there are still quite a few fantastic roms that you can flash onto your device.
Very easy actually. SBF instructions in on here and many other sites, very easy to follow, takes maybe 20 min or so, most of which is install time. (Aka, you doing nothing)
Really easy, imo. Just look at any of the rom threads and it shows the instructions of how to install. (And typically the instructions will pretty much be the same from rom to rom.)
Horrible. But that's neither here nor there, as the saying goes. Thanks for asking though.
The information I give is considered as-is, based on my personal opinion
. Use at your own risk.
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BB Bold --> Droid 2 --> HTC Thunderbolt