Shared server environment? You mean virtual hosts? mod_perl has problems with virtual hosts, because Apache/2 has limitations. For apache 1.x these limitations are there forever but for Apache 2.x I think (and hope) they soon will be gone.
The problem with mod_perl and the virtual hosts is the security. Currently Apache 2 has a solution and it's called Perchild MPM, but it's broken and development has stalled. My hope is that it will be fixed soon, because Google's summer code is starting and there is a guy volunteering to fix the Perchild MPM in three months.
There is an alternative to perchild - Mutex MPM. It's in beta, works good most of the time, but has some issues and development has stalled here too.
Another alternative to perchild is the Peruser MPM. Seems like the developers are working on it, but thats all I know.