Actually, under the CR system, the difference between levels 1 & 2 and levels 19 & 20 is approximately the same, in terms of number of encounters, relative to the strength of the party. It no longers takes months and months of adventuring to gain a mere level as it did in second edition once you entered double digit levels.
Also, you can't lose a level from casting spells or creating magic items, as far as I know. By the rules, the system forbids it. If a character wants to churn out a few items or cast a few hefty spells and raise his level, but he knows he won't have enough experience, he has to choose between gaining a level or saving the XP for other purposes. Of course, some people don't like this restriction, but that's what custom feats and/or Rule 0 is for.
The only real problem with energy drains is the meticulous backtracking of levels. For that reason, I am going to keep a copy of each character at each level in future campaigns. A little foresight should eliminate the problem.
Anyway, as a previous poster had mentioned, I think energy drains are far more lenient now (in terms of both restoration or simply making up lost ground the hard way) than they were in previous incarnations of the game. I'd to see what some folks thought of the possibility of losing levels in 2E. That could be really harsh. The possibilities were so harsh, in fact, that I never used energy drains in my 2E games. Now, however, I wouldn't have second thoughts about it.