There are very few essential differences between Whrrl and Rummble, two new social networks built on geotagging, ratings and recommendations within a trusted network, and an amphibian experience of comfortable operation on the Internet and cell phone.
Both Rummble and Whrrl pin users' whereabouts and ratings on a local map so their friends can see. Both also contain stealth settings to dissuade stalkers or shunned friends, and a manual mechanism for updating location if the phone isn't GPS-enabled.
The major differences between the reviews service and Yelp is mostly philosophical. Yelp, too, contains filters for whittling opinions to your network, and privacy settings to cloak your identity. Yet Yelp doesn't place you on a map for all to see, and won't help you schedule a meet-up as a result.
Between Whrrl and Rummble, Whrrl is much more ready for prime time than Rummble, which is still locked into a closed beta and which sports a much plainer ("faster, more universal") mobile interface. Whrrl's mapping key is also much more meaningful than Rummble's. Yet Whrrl needs a WAP site to get smartphone users to jump on board, and to improve the way information is organized on the phone. And let's not discount Rummble's fancy behavior-based algorithms for adjusting the percentage of trust you have in your friends' judgment.
Whrrl's plans for behavior-based intelligence is linked to ad support. Thankfully not the location-based targeting that pummels pedestrians with coupons as they pass a shop; rather offers associated with actual patronage.