The only thing with Namecheap is that I got a little confused when the whois guard stuff (or whatever they call it) didn't apply like it expected. My memory is a little fuzzy about the scenario right now but I bought three whois guards, applied one and then the other two couldn't be applied to my other domains. I ended up having to get support involved but they cleared it up within an hour. A little confusing? yeah. Annoying? no.
The interface isn't going to win any awards and most of my domains use linodes dns so I can't say how well their dns stacks up.
I also have a few domains on nearlyfreespeech which is quite a bit down on the interface but their terms are great.
Their DNS has been fantastic for me. Very straightforward interface, and even has a few nice touches like being able to automatically set up mx records for you if you use Google Apps on that domain.
They also raised their rates a few times. When I first joined, they were $8.88/mo. Then they went to $9.29/mo, then $9.69/mo, and now $10.16/mo. Arguably, this may be one of their downsides, but I've never minded. I believe other registrars were also raising their rates around the same time too. (NOTE: prices include the ICANN fee.)
I used to use them back in around 2004, love the company, owner is wonderful. Only reason I don't use them is I got a much better deal at Fabulous.com which is designed for large portfolios. I still recommend them to basically anyone looking for a registrar that isn't holding 100 domains or more.
In any case, I highly recommend NameCheap as well.