Reusable Applications - Architecture Question

Some times i ask my self about reusable applications, ive build several
rails/.net applications where it need a ticket system, forum and wiki.

All the time i copy and paste the code.

Now we have the Rails 3 with Pluggable Applications (well i could use
Rails Engines later, but… nevermind :stuck_out_tongue: ).

Most of the aplications i develop stay in my server, i take care if the
app is running or not, if is slow, if needs update and so.

What its a better idea in your opnion, make plugins/pluggable
applications or stick to something like SOA/Google services.

Every application in Google have a web api, this can be done to my
applications too, api to blog, forum, tickets…