I started with LR (and now have LR2), and I never got into ACR. I think I tried ACR with CS2 and wasn't a fan. I got CS5 for Christmas last year (I think? Or maybe my birthday?) so while I'm sure it's improved, I've been using LR for like 3 years now. So my workflow has always been to import and do all my basic edits in LR, export anything that I've edited as a jpg, and then continue my edits in CS5 as a jpg. I don't export RAW/DNG files because I don't go into ACR. And there's no need to export a RAW file because the LR library keeps track of all the edits indefinitely (as long as my catalogue doesn't get deleted or corrupted, lol). I only edit my favorites, or ones that I'm going to use so that I don't waste time. I also like the way LR organizes things, so that's another bonus to me.
In LR I edit for exposure, white balance, blah blah blah. The basic stuff. I pump up my blacks and contrast a touch because that's my style (and then I take it further in CS5 with my actions). I'm very used to the basics panel in LR and I tend to fight with PS when I try and do the same things in there. So for me, it's just easier to do the basics in LR and then play in CS5. I haven't gotten into using presets at all, because I have a ton of actions.
It's just about whatever you're most comfortable with. Every photographers workflow and editing style is different.