The broad-based S&P 500 (SNPINDEX:^GSPC) may be losing a bit of steam today as investors look to take profits off the table ahead of the weekend, but it certainly wasn't for a lack of positive economic data.

No story vaulted to the headlines more than the nonfarm payroll report for April, which showed gains of 288,000 jobs, well ahead of economists' forecasts that mainly ranged between 205,000 and 210,000. It was also a significant improvement from the 203,000 nonfarm jobs that were created in March. Furthermore, these additional jobs created helped push the unemployment rate down 0.4%, to just 6.3%, its lowest level in six years. More people getting back to work likely means more disposable income, which is great news for a U.S. economy that's reliant on consumer spending to grow.

If there was one downer for the day it was a slightly weaker-than-expected improvement in factory orders for March. According to figures from the U.S. Commerce Department, factory orders rose 1.1%, their second-straight month of expansion, though a bit lower than economists had forecast. This still-robust growth signals a decisive upturn following the weather-induced order weakness of January and February, and could bode well for manufacturing orders in the coming months.

By day's end, though, investors decided to take some profits, and sent the S&P 500 lower by 2.54 points (-0.13%) to close at 1,881.14. Despite the drop, the S&P 500 still ended the week higher by 0.6%.

In spite of the up-and-down market action today, there was no clearer winner than Westport Innovations (NASDAQ:WPRT), a designer of low-emission engine technologies and solutions. Westport soared 24.3% after reporting its first-quarter results, which highlighted a 39% increase in revenue, to $41.9 million (excluding joint revenue), and a 79% increase in joint revenue with Cummins.

Source: Westport Innovations.

Westport's joint venture with Cummins produced 89% more units than in the previous year, although gross margin dipped 38%, to 7.6%. The end result was a quarterly loss of $23.9 million, or $0.37 per share, which was narrower than the $0.43 per-share loss that Wall Street expected, or the $41.8 million loss recorded in Q1 2013. Westport clearly has some work to do to improve its margins and to become profitable, but the potential rewards of a cleaner-burning engine are becoming apparent with its rapidly rising unit sales. This is a company I'd suggest adding to your watchlist.

Cloud sales and marketing software developer Callidus Software (NASDAQ:CALD) joined Westport in the double-digit gainers column, advancing 13.6%, after it, too, reported better-than-expected first-quarter results. For the quarter, Callidus delivered a 21% increase in year-over-year revenue, to $31 million and, most importantly, its recurring revenue stood at $22.3 million. Recurring revenue is an important component to future cash flow, and as a software-as-a-service client to Callidus, most businesses have little incentive to leave. Adjusted income improved to $1.3 million, or $0.03 per share, reversing a year-ago net loss of $0.02 for the quarter. Comparatively, Wall Street was forecasting just $29.4 million in revenue and $0.03 in EPS. Looking ahead, Callidus expects the good times to continue, and boosted its full-year sales forecast to a range of $127.5 million-$132.5 million from $126 million-$131 million. I can definitely see the optimism pouring from shareholders today, but at nearly 50 times forward earnings, I'm not sure this revenue increase merits such a large share-price increase.

Finally, and keeping with our earnings-driven theme of the day, online marketing-tool provider Constant Contact (UNKNOWN:CTCT.DL) rallied 10.9% after its first-quarter earnings results blew by analysts' expectations. For the quarter, Constant Contact reported a 16% increase in revenue, to $78.9 million, a 170 basis point gross-margin expansion to 72.5%, a 60% increase in adjusted EBITDA, and a better than tripling in adjusted income to $5 million, or $0.16 per share, from $1.5 million in the year-ago period. Game, set, match... Constant Contact! In contrast, the Street was projecting EPS of just $0.13 on revenue of $78.8 million. The company also reaffirmed its full-year revenue forecast of approximately $330 million, and announced full-year EPS projections of roughly $1.02, about $0.02 ahead of analysts' current consensus. While no longer trading at a deep discount, Constant Contact has impressive-enough growth that more risk-tolerant investors may want to get this company on their watchlists.