Up until finishing the book my retention rate was about 80-90% on average and I was quite happy with that.

Nowadays I find that has dropped to something closer to 70-80% and occasionally I have total brainfarts and forget whole chunks of kanji within close proximity to each other. For example, last review I forgot about eight cards around frame 650 that had the fingers primitive, each of them I'd recalled 5 times in a row without fail, then I forget all of them in one session. Heh...

Am I just getting lazy or do you guys find you need to work harder to keep your memory sharp?

Cheers.

Yeah, just practice practice practice.

And read as much as you can. Hopefully
you'll come across words that use the kanji
that you have trouble remembering.

I've noticed a bit of a dip in my retention rate after a large influx of cards. I'm forgetting cards in my last stack more than cards in my 3d and 4th stack, whereas I was getting about 95% for my last stack before I started reviewing new cards. I'm thinking (and hoping) that this is due to making room for new information and that if I stay the course for a while, it'll be ok. Just stick with the reviewing and I think you'll be fine.

You should also pay attention to what kind of cards you're failing. I find that most of the cards I fail are ones that have similar meanings to others, and of course this confusion would increase as you add more cards. Make an effort to strengthen your stories so that the keywords are clearly linked to the stories and form a vivid mental image. I find that it helps to use puns (as Heisig often does) or invent names to help me distinguish kanji, like this:

悼
The Great Lamentini, an eminent magician, falls into a lamentful state of mind when he turns a volunteer into smoke and can't make her reappear.

This way, when I see the word "lament" I know that I have to remember the story about the Great Lamentini, and the only story that it fits is the one for 悼, and not 憾 or anything else.

The weird thing is, it is very rare that I fail an RTK 1 kanji these days, even though I finished the book last year. It's probably because I am reviewing kanji chains every day, which really reinforces the keywords to the point that I almost effortlessly associate the keyword with the kanji. I'm about 50% done with the joyo onyomi now (friggin' ka-gyou and sa-gyou are ridiculous), and I'm hoping that the onyomi will stick to the character as much as the keyword does.

75-100%

I finished RTK1 about 2 months ago, my daily reviews fluctuate between 20-40 cards per day, and I usually fail 5 to 8 cards out of the "4 or more reviews" each day. Some days are really good and I get 'em all, but other days are horrible, and I'll fail 5 out of 20 "4 or more review" cards.

I almost never fail a card from the lower boxes: one relearned, it stays relearned for the next 3/7/14 days.

My retention rate doesn't really change if I skip daily reviews now and then. Failing that 15 cards might feel like I'm doing poorly, but then I remember that I just passed 60 other cards, relax, and move on to the next card.

I've found my retention rate dropped a bit in the last couple of months, but for a good reason. Since the January 20 change, you no longer can boost up your recall percentage with a bunch of easy kanji you know well. Since the RTK site now does a better job of focusing on the kanji you find more difficult, you'd expect retention rates to drop, so I don't take it personally.

My pattern seems to be very similar to that of ziggr. I mostly fail cards from the last stack, and my success rate fluctuates from 75% to 95%. Sometimes the difference has to do with a more difficult batch that comes up, but mostly it has to do with my physical condition.

For instance, I noted a considerable improvement in my recall rate when I stopped taking longterm medication based on corticosteroids (which, according to my doctor wasn't supposed to have an effect in the mental area). It was actually fun that I could use the difference in effect of my kanji studies to indicate at least a strong suspicion of being hypersensitive to it.

Anyway, I now record my recall rate in my personal medical log to see if I can analyze more connections of that nature.