This feels like a very silly question, but I'll ask it anyway..

I know you can film HD footage onto mini-DV tape quite happily,

I shoot on a Sony V1E and edit with the latest version of FCP on a Mac with 4GB of RAM and 2 external harddrives with roughly 2TB of space left in total at the moment.

So what is there to stop me filming everything in HD? (I usually shoot in DVCam mode onto mini-DV tapes)

Nothing.

Except that you should experiment first to understand the kinks in capturing HDV which have been well discussed in this forum over the years.

Cheers!

Yes, once I realised you could record HD on mini-DV with no problems I imagined trial and error were the best ways forward - lots of experimentation!

I had this horrible feeling it was too easy though...!

Just so you know. Sony HDV captures with fewer problems than JVC HDV so you are past one stumbling block. Just give your shots at least 10 seconds of leeway on either side and you should have a decent time capturing. If you still have problems research the combo of DVHSCap and ClipWrap (discussed here in length) as a working solution. I use it when my FireStore DTD device craps out but I usually shoot with JVC HDV.

Once you shoot everything in HDV with the V1, you can go back to the source footage and output it to bluray once that becomes the popular medium over DVD.