We used OCaml to build a high-performance Comet-style server. It rocked. We have individual Xeon-class machines each supporting 2K simultaneous, persistent SSL connections, and pushing about 1-1.5K transactions per second at peak. I did a talk at last year's CUFP, see http://cufp.galois.com/CUFP-2007-Report.pdf, page 13. There might be a video of my talk online somewhere in the ACM's digital library.