A dumb question about ERC-4337: how many people are running bundlers today? how many user operations have been successfully bundled on mainnet so far? 

perhaps @tim or @0xstark.eth have some ideas here

Technowatermelon. Elder Millenial. Building Farcaster. 

nf.td/varun

useful Dune dashboard here: https://dune.com/johnrising/erc-4337

The founder of a YC company that runs bundlers and paymasters, John Rising (https://twitter.com/johnrising_/status/1631087378642206720?s=20) created this Dune dashboard: https://dune.com/johnrising/erc-4337

As far as bundler-as-a-service, Stackup is the only one I’ve seen. But it looks pretty simple to spin up your own bundler alongside a full node.
https://docs.stackup.sh/docs/packages/bundler/install

Last analysis I did over a stretch of a few hundred blocks, I saw somewhere around 5-7% of txs landed on chain but were not found in the mempool (most would be due to private bundles sent to block builders). This number may give a bit of intuition to your question.

https://twitter.com/erc4337/status/1631088425280618496?s=46&t=KgR4WYwCTSCbzRoZo9hkvQ