As was said, lets keep any bashing of people's ideas elsewhere. I'm all for constructive criticism and I think enough of us are grown up enough to agree to disagree on some things.
Sorry Synack, I think I missed one of your posts/replies. I'm not sure about routing between subnets, however having spent an hour discussing the same subject last night with one of the most genius networking guys I know (who heads up various technical teams at Cisco UK) we had two options: we have a cracking Cisco router provided by ISP but we're not allowed to touch it. On the other hand, any vaguely modern PC with a decent linux distribution and IP tables will outperform just about any layer 3 device under 2 grand. That's not alot, discounting layer 2+ stuff, but plenty (apparently) for a network of our size. He also mentioned STP can be a prime suspect for throttling ports too much - however we only enabled it after the problems started.
Didn't know about using STP on uplinks and RSTP on clients - what's the reasoning behind this? All the sales bullpoo just shouts "RSTP is better, thanks" with no actual information, as a result RSTP has been enabled across the board, on the units that support it (which is just the Dlink 1210-24s, not the 1224's or Procurves.) Easily done though, we have per-port control of the units.
We'll see how things transpire with the improvements over the last few days and then start seriously planning for the near future.
Many thanks to everyone that's chipped in - even the off topic stuff has been extremely enlightening and may hopefully be of use to others.