Unless you can coax dOSGi into working (which is tons of fun), then you can have services tightly coupled to other services running on entirely different machines causing frequent (and hilarious) cascades of bundle failures whenever the network hiccups.
OSGi is a trigger word for me now. I've worked on two large OSGi projects (previous job and current job) and it's always the same. Sh*t is always broken (and my lead still insists that OSGi is the one true way to modular bliss). And the OSGi fanboys always say "Your team is using it wrong!" Which very well might be true, but I no longer care. Apparently it's just too damn hard to get a team of code monkeys to respect service boundaries when OSGi makes it so damn easy to ignore them.
If I'm ever in a position of getting to design a new software architecture (hasn't happened in 10 years, but hey I can dream), I'll punch anyone who suggests "OSGi" to me right in the face.
