I am hooked on an Android chess app - Chess Free by AI Factory. It is pretty strong at blitz time controls. My guess is, 1900-2000 at blitz, and 1750-1800 at longer time controls, say 15 minutes standard rapid.
These "weakened" programs are ideal for sparring. Positionally weak, but one thing they all have in common is strong tactics. They are most dangerous when you're short of time and the position is tricky.
I think that every chess player - amateur and pro - should have some sort of computer sparring partner to play chess with. There are lots of strong programs out there that can play really high-level chess, yet can still be dumbed down to play at a more human level with two clicks of the mouse or button.
For me, having a computer sparring partner is great. Not only do you get to play chess if none of your chess-playing friends of your level or higher are around (I have none), but playing a computer also forces you to play pretty much perfectly for your skill level (yes, one can play "perfectly" for any rating, in proportion to that rating). I think my rating points had gone up about 100 points just by playing a lot of games on here and sparring with my computer on the odd day, on a regular basis.
Here's a link to the game I played with my portable computer one day. The computer is a small plastic thing made by the company Excalibur.
http://www.chess.com/blog/VULPES_VULPES/games-against-my-portable-chess-computer
So why to I write this post? Two reasons:
1. It's great to have a sparring partner if you want to hone your chess skills or sustain them. This post is my advice to you to adopt such a partner if you're like me in that regard.
2. To advertise that game - a blog post of mine - which I don't think has been getting enough attention.
Thanks for reading, and post your thoughts on this matter below!