Using the option key (mac) to show masking effects while sharpening works in Lightroom 3 and 4. Adobe lifted a lot of ACR features for LR so it tends to combine major pieces of Bridge and ACR into one package and have a lot of the same shortcuts.
Noise reduction and sharpening in LR have become much stronger and are, like all of LR, non-destructive, so if you overdo it, you can back stuff out. If you apply lens correction in LR it will set a certain level of NR and pre-sharpening and part of that process. I find that if I want the best results I use an external plug-in like Nik's Define and Sharpener Pro on copies, but often can do close enough for initial proofing all in LR to get a good sense of how well the shot is going to stand up to various levels of NR and sharpening.
Totally side with the reduce noise first, then do a little pre-sharpening early in the work flow, and sharpen for final intended use last.