They definitely improved since the takeover by JaguarPC. I think the problem was that Resellerzoom had grown too quickly and it was started to show some "cracks" in serverload and support (response time). I have noticed a lot of improvements since the takeover and I am still a happy customer.
Have been a customer of RZ since almost 5 years now, first on a budget account and later on a UK-account. Before I found RZ I had tried out a lot of different providers and was always on the lookout for a new provider but ever since I have been with RZ I have not been looking anymore. Sure, I still read this forum to keep an eye on the movers and shakers of the industry but that is only common sense. Just like always keeping your own backups.
Support has been great and always helpfull, never had any problems with billing and there have been a few (minor) issues but they were always fixed quickly.
For any company the size of RZ you will find positive and negative reviews, that is only to be expected. The best you can do it try them out for yourself, they have a 30 day money back guarantee.