You see it all across Silicon Valley. Our largest tech companies booming, hiring thousands of new workers, and hoarding ever larger piles of cash.

At the same time, our local communities and governments are fighting to keep their heads above fiscal waters, cutting back on services, slashing employees, closing libraries.

With this disconnect growing, it's been heartening to see the way Facebook has embraced its role in its new hometown of Menlo Park. The latest example of Facebook's laudable efforts to increase its local economic impact arrives after Thanksgiving with a new program the company is launching called "Facebucks."

Facebook plans to distribute Facebucks, essentially $25 gift cards, to employees to use at designated local merchants in downtown Menlo Park. While it's still uncertain just how much financial impact Facebucks will have, the symbolic importance is huge.

"It's a good idea, and I applaud them doing it," said Menlo Park Mayor Kirsten Keith. "This kind of commitment is also unusual. We're very fortunate to have them here."

The Facebucks program was written into a larger development agreement the company signed with the city of Menlo Park earlier this year in exchange for being allowed to employ more people at its campus than the previous occupant, Sun Microsystems. Facebook agreed to pay millions of dollars to make up the difference between the sales taxes Sun generated, and the lower amount of taxes Facebook is projected to create.

This is a common misperception: that just by landing a big employer like Facebook, a town's coffers will fill with new tax revenues. If that were true, Silicon Valley's local governments would be the most prosperous on the planet. Instead, too often, they go begging.

Part of the issue is that the state of California only levies sales taxes on physical goods sold, not virtual ones. As our lives have become more digital, and as bookstores and records stores have shuttered, local governments have taken hits.

Sun, because it sold servers, generated big sales tax revenue, part of which went to Menlo Park. By comparison, companies like Facebook generate little or no sales taxes on the ads they sell. Rather than trying to duck responsibility, or squeeze Menlo Park for other incentives, Facebook offered to pay millions over the next decade to make up the difference in sales tax collections.

But part of the economic promise of these big companies is that the thousands of employees they bring will move through their towns, spending money on coffee, meals and clothes, which in turn generate more sales taxes for local towns.

Yet the campuses occupied by many of the largest companies can also become islands that cater to an employee's every need. Many employees who take the train to Menlo Park then hop aboard a shuttle that takes them to Facebook's headquarters.

Why journey three miles to downtown Menlo Park when there's free coffee on campus?

"When we moved to Menlo Park, our employees had been very familiar with downtown Palo Alto," said Lauren Swezey, Facebook's sustainability and community outreach manager. "We wanted them to connect with downtown Menlo Park. We want them to get to know their new hometown."

Swezey said part of the goal is to get employees familiar with the shops in town. That same shuttle is available to whisk them back to downtown Menlo Park to shop or eat. Facebucks are an extra incentive for employees to make that trek. And the company plans to encourage teams of employees to hold meetings off campus, using Facebucks for meals.

Facebook has partnered with 15 local restaurants and shops who will accept the Facebucks cards. One of them is Menlo Velo Bicycles, owned by Rainer Zaechelein.

He said he's been pleased with Facebook's commitment to local merchants. Even before Facebucks launches, Zaechelein said the company has made his shop one of the primary vendors for providing parts and services to the fleet of bikes it keeps on campus. He's also been involved with efforts by Facebook to encourage employees to bike to work, and planning for upgrading bike trails.

As a result of those efforts, he's already seen an increase in customers who are Facebook employees. In addition to accepting Facebucks, merchants will offer additional discounts or deals. In the bike store's case, employees using Facebucks can get an extra 10 percent off bike accessories.

"I think it's a great thing for a company like that to give back to the community," he said. "I can say that even in the short amount of time Facebook has been there, I've seen more of an impact from them than I ever saw from Sun."

Facebook also agreed to invest in a number of physical improvements to local trails, and in efforts to reduce traffic impact. Held up against these much larger investments, the actual dollars (Facebook is still working out the final details of how many cards will be distributed, and how quickly) that flow from Facebucks are likely to be smaller. In the coming months, Swezey said the company will be monitoring the program closely, see how it is -- and isn't -- being used.

"We want to see this money spent," she said. "We don't want these to sit in someone's drawer where they're forgotten."

Whatever the ultimate numbers and direct impact of Facebucks, the program is reinforcing an important message that just can't be amplified loud enough: We need our biggest companies to take seriously their obligations to support local economies and governments.

They must understand that over the long run, the future of Silicon Valley depends on having both strong employers and healthy, thriving communities. We can't have one, without the other.

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I also wanted to share some personal news. This is my last column for the Mercury News. In my 13 years covering Silicon Valley, I've lived through the dot-com bubble, energy deregulation, the housing meltdown, and the rise of Steve Jobs and Apple (AAPL). I've also seen an endless parade of fascinating characters and innovative technologies. It's been my honor to be one of the Mercury News' columnists the last four years and sincerely appreciate the many readers who have followed along, screamed at me on many occasions, and sometimes offered a pat on the back. All I can say is: "Thanks."