This is an often-discussed topic at the AVS forum. Here is the Replay forum. There are many threads that compare the current features of replay and tivo -you will just have to ignore some flames on which is better.

Some features in the current Replays not previously mentioned in this thread:

-Replays have an Ethernet jack, so you can easily transfer/archive/burn to disc recorded shows.
-Replays have automatic commercial advance. It will automatically skip commercials (*no* remote clicks required).
-Replays can send shows over the Internet. Planetreplay.com aggregates and index of content from hundreds of replay devices. Its simple to email others requesting shows that may not even be broadcast in your area.
-With multiple replaytvs in one house, the content of all the replays are shown in each replays guide. You can play back shows real time that were recorded on other replaytvs.