Shivaram-
We personally have not gone so far as to use another tool, since in my personal opinion LoadRunner is by far the best platform available for performance testing.
Instead, we adjust estimates for script development accordingly and continue to use the Web (HTTP/HTML) protocol for primary side load placement. Correlation can be much more complex on some of our newer internal application platforms which use extensive json/comet calls, but the end product can still be made to function predicatably and reliably.
Then, to capture any client-side metrics, we can still use a very small implementation of a couple GUI-type virtual users such as TruClient.
Regards,
-Andrew