The tactical site problems are fun, challenging, and I can definitely see some improvement. That said, I still have quite a bit of trouble seeing some of the tactics in real games. The reason I think this is is because I know that there is something creative I'm supposed to do on the tactics website. I have a harder time finding it when I don't know it's their. When I put my games into Fritz for analysis a lot of times I end up saying to myself "Damn! I should have seen that." I suppose it will take more time for me to get better board vision. Or maybe I should just resign myself to mediocrity when it comes to chess.
I found it useful to go through Reinfeld's sacrifice and combination book in a shuttling fashion. That is, i'll do the first five in one sitting. In the next sitting i'll start from the first and do ten, then later start from the first and do fifteen. Usually the ones i have already done come quickly, but the repetition is useful. I don't know if i'll ever get to the end. An annoying thing about the book is i got it used from ebay and it still has descriptive notation and some of the pages have smudged diagrams, like playing chess in mud. It's still a great book, and can be gotten for a song.