At a press event in San Francisco this morning, Microsoft demonstrated recent, brand-new, and upcoming features it’s adding to its Bing search engine. The big news: The company is launching a beta of a major upgrade to Bing Maps. The beta is available here–and for the sake of comparison, here’s the existing version of Bing Maps, which remains the default.

From my experience so far, the new Bing Maps may be a true beta in the “we’re still working on making it work” sense: It sometimes performed very slowly, or conked out altogether. (Disclosure: I’m trying it on an EVDO connection, which probably doesn’t help.) The new version requires Microsoft’s SilverLight browser plug-in to work, which will be a source of controversy: There are folks who dislike plug-ins in general, and some who have a particular distaste for SilverLight. And since SilverLight is far from universal, there’s a good chance you’ll need to install it before you can test-drive the new Bing Maps.

It is, of course, inevitable that any discussion of Bing Maps will use Google Maps as a frame of reference. The new Bing Maps preserves some features that Google Maps doesn’t have, such as birds-eye aerial photography that shows cityscapes in perspective, not from above. It finally adds a counterpart to Google’s Street View street-level photography: Bing calls its version StreetSide, and it’s available for 100 U.S. metropolitan areas to start. (The interface is really similar to Google’s down to the use of a doppelganger of Google’s Pegman to help you navigate your way around.)

And it tries to surge ahead of Google Maps in some respects–my favorite of which is Map Apps, a series of optional map overlays provided by Microsoft and others. They include everything from maps of major world cities to offbeat roadside attractions.

Oh yeah, there’s also a Twitter Map app, which lets you view Tweets for a neighbourhood you’re perusing–pretty nifty.

The new Bing Maps also integrates Microsoft’s clever Photosynth 3D photo collage feature.

But clumsily so, at least in my encounters: It devotes prime real estate to promoting Photosynths near your geographic searches,

but doesn’t indicate what the Photosynth is of until you click on it.

(When I did a search for San Francisco’s Fairmont Hotel, high atop Nob Hill, Bing Maps kept urging me to view a Photosynth which turned out to show Union Square.)

So is there any benefit from Bing Maps’ use of SilverLight, versus Google Maps, which depends on open-standard AJAX programming techniques and doesn’t require any browser plug-ins? Yes, at least a little: Bing’s maps zoom in and out more fluidly, and wandering around StreetSide views provides a more smoothly-rendered experience than Street View, which can get choppy. SilverLight also enables the Photosynth integration. I said in a Tweet that the new Bing Maps might be the first (non-Olympics-related) SilverLight app good enough to induce a lot of people to install Silverlight, but now I’m not so sure: I want to see if the slow and erratic experience I’m getting is a temporary quirk or an ongoing issue. (And if you’re the type with a deep, instinctive dislike of plug-ins, I’m not sure that there’s anything in Bing Maps that’ll make a believer of you.)

In any event, I’m rooting for Microsoft to keep plugging away at Bing Maps in particular and Bing in general until the world sees them as serious rivals to Google’s offerings. With Yahoo’s planned exit from the search innovation wars, Bing is the closest thing that Google has to serious competition. Even if Google remains the leader, I’d love to see it running scared, at least a little bit.

If you check out the Bing Maps beta, let us know what you think.