I'm sitting at 4.1U and everything I've seen so far suggests that you not upgrade to 4.2 just yet. It still sounds to me that there is no brick protection that's 100 percent secure on that level yet, and 4.2 really gave us nothing. I'm just saying be careful. Use bootmii as boot2 if you can, and definitely 1) back up your NAND, and 2) NEVER DELETE IOS FILES, ESPECIALLY IOS60!!!!
That said, I modded mine (with fingers crossed) again last night using the Wii Shop and Mii updater file from Wii Brew. It tells you if IOS61 has been updated - mine had, so I skipped that step. Then it asks you if you want to update the Wii Shop channel first, then the Mii Channel. Wii Shop takes quite a while to fully load the mod, be patient....but no problems with either, and I can finally get to WiiWare again (hello, Lost Winds 2).
The whole point of the second paragraph was to say this: if you don't trust 4.2 yet, there are ways to mod the Wii to include the new versions of channels WITHOUT doing a full system upgrade - and you might want to try that first. Just my two cents based on my readings so far...