You can still use TiVo's with DirecTV. We have an HR10-250 HD unit still and a couple of the SD DirecTV TiVo's.
Mind you we do have two of the newer HR20 HD units also that directv makes, and I will be honest they have gotten to the point that they are pretty darn nice.
Actually DirecTV and TiVo announced awhile back that TiVo is making a new DVR for DirecTV users. So in a year or so you should see a new DirecTV capable TiVo.
I am a huge TiVo fan so I am interested in this new DVR (probably a year off), but am happy with the HR20's right now. They are very fast. The UI is not as nice as TiVo but you can set season passes, organize them, and do it all very quick.
The DirecTV HR20 family of units has some newer features added too like remote scheduling over the web, ON Demand downloads from the internet right to the hard drive, support of UPNP DLNA servers (for audio and video playback), ability to view content from the DVR's on your PC (currently Windows only, but hopefully some Linux hackers figure it out). They are looking at the ability to share videos from all HR20 family DVR's on any other ones in the house too (over the network). There is also a open beta test feature where if you follow the dbstalk forums you are alerted to beta versions of software for the various HR20's. You can reboot your receiver during the beta test download windows (usually 11pm - 1am EST) on specified nights and hit some codes on your remote as you reboot to force the download of the beta software. Has been great for DirecTV to get feedback on new features. If you don't like the beta or have problems with it, just reboot and force a download outside the beta window to get the normal release version.
Mind you I really love TiVo's but even their new HD units for OTA and cable/cablecard reception don't have as snappy a UI as I would like. I started using TiVo's way back when they had their first 14 hour unit. In fact I was the guy who wrote BlessTiVo which was the first program (it was a linux program too obviously) to automate formatting a second drive for your TiVo to allow users to expand their TiVo's storage. Even got interviewed by CNET way back.
http://news.cnet.com/2100-1040-244104.html
So I am eagerly watching to see what this new TiVO DirecTV unit will be like. I am hoping it has the multi room viewing, remote scheduling, PC viewing (and we can get it working with Linux), etc. But I fear DirecTV won't let TiVo put something out with all those features to put it on par with their own units, and have that TiVo interface.
Regardless you can still use TiVo's on DirecTV. But honestly the current DirecTV units are pretty nice, and are really fast. One of my favorite features is for setting up a season pass you just highlight the show in the guide, click record and it is set to record that one show. Click record a second time and it automatically sets up a season pass to get em all. You can tweak the season pass later if you want to change how many it keeps, if it should get reruns, etc. But I just set the defaults to be what I normally want, so when I do the two click record I have a season pass in a second. Also when you reorganize your season passes and exit that screen it rearranges and exits immediately. The TiVo has that "please wait" message that take a minute or so depending on your season pass size.
Another nice feature is if you have a bunch of shows recorded from a season pass and you want to dump them off to your PC with a capture card (be it SD or HD capture) you highlight the season pass folder with all the episodes in it, and instead of going into the folder to play specific episodes you just hit the play button on that highlighted folder and it plays all the shows for that season pass that have been recorded one after the other. So you can set your capture card to record a long block of time and get all them in one capture. I use this for our littlest one when I record a bunch of her favorite cartoons , knock out the commercials and put the files on my server so she can have easy access to them.
I remember seeing on the dbstalk forum a picture of a Microsoft testing lab with a bunch of DirecTV receivers that connect to a PC. It is a product that exists, but has never been brought to market yet.
Also an unrelated tip (to an already long post).
Costco has a Philips DVD player that is an upconverting player. So it has HDMI outputs and all. But it works equally well with SD TV's. Nice thing about it is that it plays videos in file format on media also (be it a burnt CD, DVD, or USB device). I have thrown DiVx files at it, MP4 videos, and even a few WMV files and it has played them all. You can also plug a USB memory stick or USB hard drive into it and play any of those files off that device also. It is around $40 -$50 or so. Does MP3 and all that jazz too. DVP-5992 is the model number. Bought some for family at Christmas and they love them. Put the entire season 3 of Dexter on an 8GB memory stick and the wife watched them over the holiday weekend.