I'm running it on the Asus WL-520GU, and haven't had any issues.
I've also recommended an MLPPP setup to a client company of mine, and have purchased the ASUS WL-520GU to act as the front-end router that will sit just in-front of the corporate firewall.
Obviously, right now, since the deployment of Multi-link PPP is not widespread, most small to mid-size equipment vendors have chosen not to include support for MLPPP in their products (SonicWALL, Cisco Linksys, etc.). However, Routerboard supplies an enterprise-class product that apparently supports MLPPP deployments of up to 5-bonded lines: »www.routerboard.com/pricelist.ph···oduct=90
The MRRP is roughly $70 USD, so it's actually pretty cheap considering the capabilities. I would rather deploy this product, as opposed to Tomato, because it is "officially" supported by the vendor, and routerboard's products are known for performance and stability.
I know there are a few others on here testing out the Routerboard product, so maybe they can fill you in on the details, as I have yet to actually test one out for myself.