Nigelondraft - that's a very good point and something I'll certainly bare in mind. I was always trained to give speed instructions well in advance on TOD to ensure, like you say, that your descent can be planned accordingly, and for the most part I do this (usually only unable to if traffic is bunched and all aircraft arrive at or past TOD at the same time, which happens annoyingly often).
My post wasn't so much referring to these sorts of scenarios. I was thinking more of the occasions when speed instructions are given well in advance of TOD (like with the B734 previously mentioned), but are still ignored.
Another example that springs to mind from 6 months or so ago was a business jet (C750 perhaps?) given a speed restriction of 270kts or less when he was cruising at FL400 and at least 30 miles from TOD. The pilot flew at mach 0.85 (or something similarly high) until FL230! IAS was around 340kts if I remember correctly. His excuse was he hadn't transitioned to IAS yet. This too makes no sense to me. 270kts or less is 270kts or less. It applies at any level, even when flying with reference to mach, simply meaning IAS never greater than 270kts. Perhaps I'm missing something but how can that be misinterpreted?