Here's an Elgg based dating site: https://myfreepersonals.com/

It doesn't have much in the way of theme, but it's got customized profiles and an effective geosearch.

Speed - out of the box Elgg is alright, but slows down quite a bit with high usage due to some inefficient parts such as search.  There are ways of dealing with it and making it more scalable, but they take some effort.  That's something you don't need to worry about until you need it though, but know that it can be done.

Plugins are easy to write for Elgg, that's the biggest draw (for me anyway) - you can do pretty much anything with it.

"Dating site" tells us nothing about what you'll need to build. Choose the programming language your devs are best in. Elgg requires good PHP skills.

Elgg pros: big supply of free plugins; powerful plugin API for fast (IMO) development; good APIs to support social interaction; and good commitment to not breaking plugins on upgrades.

Elgg cons: out-of-the-box UX/UI is showing its age (will require professional theming work); not much ajax in built-in features; hard to judge high quality plugins; some backend APIs are slow.

Hey Matt thanks for sharing the example site. I registered there but in a short time only it's clearly observed that it's pretty basic with very few customization. My requirement is lots of customization and lots of enhancements on top of default functionalities.

Steve- thanks for explaining the strengths/weakness of Elgg with small words.

Overall it seems that Elgg has lots of potential for developing social sites especially dating sites. But there will be lots of effort to make it very professional looking. 

Now which one is preferable(buddypress/Elgg) is still a point to be clarified.

Anyone who can provide some more insight please be kind enough to share your thoughts

Regards

Praty