With 4E, however, I've abandoned XP tracking altogether and now I just level the PCs up each time they complete an important objective.
Strange to say, 4E is the first edition where you can do this with no problems and no tweaking. In 3E, it was almost possible without tweaking, but you still had item-crafting spellcasters to worry about, not to mention level drain. Previous to 3E, of course, every class ran on its own XP track.
This is absolutely true - 4E is the first system where you can do this without worrying about xp spent for making magic items (in 3.x), or the different progression rates of the classes (1st & 2nd).
Initially in my 4E game I tracked xp for quests, skill challenges, and encounters, and kept it all on a spreadsheet. I told the players how much xp they had at the beginning of the next session.
I started with RP bonuses just as we had in our 3.5 game, but found the same people were getting them all the time because they tended to RP more. The bonus xp didn't do much to encourage roleplaying among the group - it just created an xp disparity between the characters. (As an aside, a means of encouraging roleplaying that has worked for us so far is the use of aspects and fate points, a la SotC - but that's another topic.)
With 4E, it felt better to have the entire group level at the same time, so I dropped the RP bonuses to specific people, and instead wound up giving bonus xp to the group in general. By then, I wasn't telling the players their exact xp totals, although I was still tracking them in my spreadsheet. I told them when to level up based on the totals I had. Finally, when I found myself tweaking my bonus xp totals up or down so they would level at a good time, I realized there wasn't any point in tracking xp. Why do unnecessary bookkeeping?
We level when it seems right - about every 4-5 sessions, and when major objectives have been completed. I still use the xp values in setting the difficulty of a given encounter, but that's all. It's nice to not have to track it, and I prefer to have the group level together rather than some people eventually outleveling their companions due to differences in the way xp happens to be awarded.