Does anybody have any experience with MS Lync? Has anyone tried integrating it with normal phone / VOIP services for a unified communications platform?

I've got it running here, integration is "fun" if your phone system isn't on the supported list as it really wants to do everything itself.

If you're happy using soft phones or MS lync ones then it's not bad

I've set up more than a few Lync systems in my time. IP Telephony can be a bit of a horror, the best thing to do is get your telephony supplier to install an SBA or media gateway wherever your servers are, that makes things a whole lot simpler (although they'll charge you a monthly fee for it most likely). As Saspro says, it makes life much easier if you just stick to the stuff MS recommend.

Thanks.

Our phone system is reaching the limit for "normal" digital phones, so we would have to add VOIP phones, but that means a licence per new extension, as well as the phone and PoE switch, so I'm looking at alternatives, from on-site VOIP to cloud VOIP exchanges. It is difficult to compare the offerings though...

I was looking at possibly using Lync as an extension to the VOIP system, either using an external VOIP provider and using Lync internally or using a cloud VOIP exchange and extending the internal side through Lync for video conferencing, IM and desktop sharing.

If you've hit your limit on your digital system I'd say get some sip trunks from your telco then run Lync on premises.