MPLS isn't really a replacement for an IGP routing protocol like OSPF. Its more a complementary technology.
What was the exact benefit that your OSS vendor gave as a reason for adding MPLS to your network?
Like Inssomniak, I'll tell you what I used MPLS for in my previous job.
We used MPLS for L3VPNs to keep the management network for our WiMAX network "contained", as opposed to mixing it in with the management network for our POPs.
Along with this we also sold L3VPNs to some customers to link offices together, and we also did some pseudowire stuff to provide "a really long ethernet cable" to some specific customers.
said by unwired :
My understanding is the switching the mpls would provide would be more efficient than routing the pppoe clients over ospf.
Kind of. But it may not be noticeable with a small network. And you're still going to need to run an IGP anyway.
In BIG carrier networks, MPLS makes more sense for moving traffic through the very inner core of the network because its a much simpler method of switching packets compared to IP routing, and as a result, the very core devices can be really "simple" and move lots of data really quickly.
Also you dont really "route over OSPF". OSPF is just a protocol that talks to neighboring routers to share routing information that it uses to work out how to get from one part of a network to another. That information is populated in to the FIB of a router, and the router then forwards the traffic.
You could think of OSPF as like phoning a friend to ask what address you should write on an envelope to post a letter to them.
Routing would be the postal service then does the delivery, routing the letter through its facilities and delivering it to your friends mailbox by reading the address you have written and using that to determine how to route it.
MPLS could be thought of in a similar manner, but instead of writing an address, you stick a barcode that describes the destination on the letter instead. The postal service then very easily decodes the barcode to determine where to send the letter next. They can do this much quicker than trying to read the address you have written on the envelope, and as such equipment will be much simpler, and it will process more envelopes.