I'll chime in.
I have 2250 installed in an HTPC, and only using it for OTA ATSC. I have a DB4 antenna in the attic, and it feeds via amplified splitter to the PC and 2 other HDTVs. I have XP Home, latest drivers for the card. Btw, I heard nothing but woes from 64bit OS users. I think Hauppage drivers don't like 64 bit.
WinTV(any version of it) is utter crap. Ditch it.
As I have XP Home, and did not want to change my OS, I opted for a 3rd party PVR software, and I went with SageTV. It rocks.
The scanning process is really no good - not sure what to blame here, hardware of software. A digital channel scan gives back a paltry 2-5 channels. HDTVs scan same input and get a full gamut of channels. However, when you try to tune into a channel manually using proper physical channel number (i.e. WCBSDT 2.1 physical channel is 56 so full channel designation is 56.2.1), it tunes into it beautifully. What this means is one needs to spend about 30 minutes to manually map all the channels to their proper physicals. A pretty simple thing to do in SageTV, not sure how WinTV or any version of MC does it. Once I set it up, it has worked great. I set the recording quality to best - so it records full 720p MPEG2s with 5.1 audio, about 3GB/hour. If your recordings look bad, check your quality settings.
About the problem where screwing the cable tight caused problems: appaently, the antenna connector on 2250 is flimsy, and tends to snap off when it has to 'fight' the thick rigid coax cable. Chances are yours has snapped off and is really held by central lead only - and when cable is not rigidly attached, the connector can 'reseat' itself for proper contact. Mine also snappped off, and I fixed the problem by using 2 retainer nuts to rigidly couple it to the card's backplate. If you are planning to buy the card, I really advise you get a couple of those nuts from Home Depot or Radio Shack and secure the antenna connector to the back plate BEFORE it snaps off. (Remove the backplate, thread one nut on the connector, reinstall backplate, thread on 2nd nut, tighten nuts against backplate)
Those aside, the card is a solid performer when used with good software.