Most people are happy when one of their stocks zips up 9% in a day. Most people are elated if it's one their larger holdings.

But, as often as I wish it -- and hair-envy makes it very often -- I'm not like most people. That's why today's jump in SanDisk (NASDAQ:SNDK) shares has me scratching my bald spot and looking the gift horse straight in the choppers.

Sure, over the weekend SanDisk released news that it has doubled capacity on some of its card lines, but that's not what's moving the stock. Nope, I think it's probably the upgrade from Citigroup, whose report I haven't seen, but which reverses a 5-week-old downgrade (to hold) from the same group. Before that, in December, the big C upgraded SanDisk, having downgraded it in October.

Now, I don't normally pay much attention to upgrades and downgrades, or analysts who make them, especially when they come as often as these. It's too bad I need to come to that conclusion, because I'm darn sure that Citigroup SanDisk analyst Craig Ellis knows a lot more about this company than I do. (I bet he's got more hair, too, but I digress.)

Yes, it's very unFoolish of me not to poke fun at an analyst when I get the chance, but on this occasion I must beg off. Ellis routinely asks some of the better questions on the SanDisk conference call, the kinds of things that draw out very useful answers.

But that doesn't mean that Ellis (if this is his call) or the team at Citigroup can't overthink.

Really, does Citigroup know anything more than it did 5 weeks ago? I doubt there's been a drastic change in SanDisk's prospects for selling MP3 players and flash cards to Best Buy (NYSE:BBY), Costco (NASDAQ:COST) -- where I see them prominently placed -- or original equipment manufacturers like Motorola (NYSE:MOT). As we found out in the last SanDisk call, the firm is slightly ahead of pace with its new wafer fabrication plans, so it has decided to use the cost savings in raw memory to push down prices fairly aggressively on end products, in order to stimulate demand. That will mean good deals for those of us who shop the retailers mentioned above in order to feed the appetites of our Canon (NYSE:CAJ) cameras and Palm (NASDAQ:PALM) handhelds, not to mention our Xboxes, laptops, and the ever-growing list of flash-gobbling gadgets. In fact, I just cashed some SanDisk rebate checks last week...

But I don't think this means problems for SanDisk. However, that fear is what panicked the market at the time of the announcement -- the dread disease of margin waste. This is a valid concern, but I note that SanDisk has used this pricing pressure successfully -- and profitably -- in the past. In fact, its business model sort of depends on it.

Where does this lead us? Maybe nowhere, although I'll take that gift from Mr. Market today (thank you). I know deep in my heart of hearts that one person or one bank's opinion doesn't make SanDisk worth an extra billion bucks. Maybe Mr. Market just needed his hand held. Or maybe, just maybe, the last big haircut was overdone.

Seth thinks SanDisk is just the kind of up-and-coming market leader that would make a nice fit with Motley Fool Stock Advisor, along with current picks Palm, Costco, and Best Buy. So far, Tom and Dave have resisted SanDisk, but they've got plenty of other ideas. A free trial will get you a look at all of them.

Seth Jayson is happy with his SanDisk products. At the time of publication, he had shares of SanDisk, which also makes him happy, but he had no positions in any other company mentioned here. View his stock holdings and Fool profile here. Fool rules are here.