Got hosed because I accidentally added a a clause in our "how backed up are we" from http://thebakingdba.blogspot.com/2010/10/replication-better-alternative-to.html , and set it up wrong, so I filtered stuff I didn't mean to.
Lessons learned, and got me thinking ... One thing I haven't had on my replication monitor was a reliable way of detecting if any of my subscriptions are expired or about to expire. The dread 72 hours. So, several hours later, a profile trace and a question on StackOverflow, and I got a way to do it.
Basically, you're running the system SP sp_replmonitorhelpsubscription, once for each server that the distributor handles. You then filter that out (looking for warnings and ignoring recent records) and send an email if there's anything left.
One downside: because we're trying to avoid the NESTED EXEC issue (can't have an INSERT INTO EXEC where the code you're running has an INSERT INTO EXEC), the most reliable way to avoid it is by using OPENROWSET (thanks to Paul Ibison for that). However, that requires that Ad Hoc Distributed Queries be enabled via sp_configure. Yes, it can be a security hole.
An alternative way to do it, according to replication expert Hilary Cotter, is to run the SP twice, and only INSERT INTO on the second Exec. In my testing it's not as reliable (fails occasionally, and doesn't lend itself to automation quite as well, but it may be a better option for you.
Hope this helps (and hopefully the blogspot sourcecode formatter I'm using is good)!