I've used two ISPs with LimeWire:

Speakeasy DSL specifically states that they aren't blocking any ports, and specifically allows running servers and P2P applications. I was using SpeakEasy until the cable company came out with a better deal for landline phone than any phone company could come close to matching, so I had to drop to landline, which meant dropping DSL. Actually, cable is way faster than DSL around here (NY Metro).

Optimum Online (cable) prohibits running servers in their TOS/AUP, and they consider running a P2P client that shares files to be a server. If they notice that you're running a server (e.g., LimeWire), they don't do any port blocking but they have been known to impose a 150kbps (~15KB/sec) upstream cap on your data connection if they feel that you're abusing the network connection (mostly on the upstream side of things; they don't seem to notice as much if you're doing lots of downloading (it should be noted that the current cap for OptOnline users in the NY Metro Region is 10Mbps downstream and 1Mbps upstream). If you intend on sharing files, I'd suggest setting the max upstream rate within LimeWire to somewhere around 25kbps, and half that speed during business hours (e.g., 7am-9pm).