Let's step in the time machine and go back to the end of January. When last I wrote on SirenzaMicrodevices (NASDAQ:SMDI), I said, "I'm going to wait for a swoon in the stock before buying".

Uhh, yeah ... good plan there.

A stock that I kick myself for not buying at $3 or $4 throughout 2005 was trading at $7 and change back then. Now those shares will run you close to $12.50. And sadly, paper profits are not recognized as legal tender by your broker, your bank, or major retailers.

While there might be some froth and hype in this stock now, it's not just hot air that's pushing it up. Revenue in the recently completed first quarter was up 72% on a year-over-year basis and up about 7% sequentially. Simply put, it pays to have fast-growing and/or powerful customers like Motorola (NYSE:MOT) and Sirius (NASDAQ:SIRI) using your products. Margins also improved, and the company posted strong earnings on both annual and sequential comparisons.

But wait, there's more.

Though pricing was a little soft sequentially, management's comments make me think it was largely a mix issue. Further, 80% of this quarter's business has already either been shipped or logged as a firm order, so I've got to think the odds of a major revenue-driven disappointment aren't that great.

And the future of course still looks bright. The company made a meaningful acquisition that will, among other things, give it exposure to the cable TV market and companies like C-COR (NASDAQ:CCBL) and China's Huawei. Of course, there's also sex appeal from WiMAX opportunities, 3G rollouts, and a larger chunk of business tied to Sirius.

So now for the tricky part -- the stock price and its valuation. I've said before that traditional cash flow modeling doesn't work well on these fast-growing companies, since you're likely to either dramatically undercut their potential or grossly overestimate it. And so that leaves you with fuzzier methodologies like future P/Es and price-to-sales ratios. But for investors who like high-risk/high-reward/high-growth stories, "fuzzy" is often good enough.

I'm tempted, very tempted, to just hold my nose and buy into the growth. Then again, looking at Genesis Microchip (NASDAQ:GNSS), a completely different company in a completely different market, maybe there's nothing wrong after all with making some money in boring stock sectors like steel and industrial conglomerates.

For more fast-growing Foolishness:

Looking for the next great tech innovator? Our Motley Fool Rule Breakers newsletter can lead the way. And now you can take the swashbuckling newsletter dedicated to up-and-coming companies in emerging fields for a 30-day free spin .

Fool contributor Stephen Simpson has no financial interest in any stocks mentioned (that means he's neither long nor short the shares).