As I have gleaned so much valuable info from this site, I thought I'd share my experience this evening!
I've been soft-modded for a while, but stuck with 3.2E for ages. I recently decided to update to 4.1E and did so using the excellent guide on this forum. That all went well except for the shop channel giving me a black screen despite many attempts to install and reinstall. Tonight I updated to 4.2E using DOP-Mi v12. I knew everything was backed up already having only just gone to 4.1 so just jumped right in and updated to 4.2. After that I used DOP-Mi to reinstall IOS-61 followed by a reinstall of the Shop Channel. It worked fine, so I proceeded to download the Internet Channel and I-Player from the Shop - both also working fine.
Other tests done tonight include:
I loaded Rock Band 2 from the disc channel (original game disc) and the game and instruments are working fine (that was the first time it had been played on this particular Wii).
NeoGamma R8 loaded up a couple of back-ups and I also used it to load an original of Super Smash Bros - all working fine.
Wii Speak channel installed using DOP-Mi and working fine (mic working in channel but not tested in game yet).
I also decided to chuck in an original of Super Mario Bros - it showed 'Sytem Update' in the disk channel and I decided to run it (I couldn't resist!). The update ran, the game loaded fine and everything else is still working!
However, I have noticed that PriiLoader v0_3b has no hacks in it's list anymore - I assume a newer release will remedy this! I also haven't used a USB hard drive!
So anyway, ..... so far so good!