I agree with you that Clif and Luna Bars are very tasty...but to use them as meal replacements in order to lose weight? I wouldn't.
In my opinion, there are WAY too many carbs (up to 39 grams, 18 from sugar!) and far too little protein to do anything for weight loss. In fact, nutritionally speaking, it's about the same as a Snickers Bar as far the protein/carb ratio goes.
In fact, Clif Bars aren't actually marketed for weight loss. Like Power Bars, they were developed, marketed, and targeted toward athletes/athletic people, who need a big jolt of carbs while doing intense long-distance sports such as cycling, marathon running, or hiking, which they burn off during the activity. Unfortunately, for the 90% or so of us who AREN'T doing those kinds of activities regularly, eating Clif Bars or similar high-carb nutrition bars is just going to give you a huge unneeded jolt of sugar then go right to your thighs..
There are worse things you can eat (actually the Slim-Fast nutrition bars are in that category!) but I wouldn't eat Clif Bars on a regular basis...unless you're running a marathon or training for a highly aerobic sporting event!
BTW, the new magazine "Energy for Women" has a TERRIFIC article reviewing and critiquing different nutrition bars. Recommended reading - here's what they had to say about Slim-Fast bars:
This is the only bar on the market that actually makes me angry. The nutritional content of the SlimFast bar is no better (and in some cases worse ) than most candy bars. I'd just as soon see you eat a Snickers bar. At least Snickers provides some real peanuts and good fats to slow digestion and moderate its blood sugar effects. And Snickers makes no bones about the fact that it is a candy bar. The SlimFast bar, on the other hand, is sugar mixed with sugar, surrounded by fat and sugar - and then has the audacity to claim to be "The delcious and nutritious way to lose weight and stay fit." I'm guessing that the marketing folks at SlimFast must get a monthly supply of Valium as part of their pay. I don't know how else they could sleep at night."