They filter/firewall residential DHCP service to keep you from running servers (http, https, ftp etc) but they don't tell you this directly.
The only port I've found blocked is SMTP. I ran servers on 22, 80, and 443 plus others for a long time before I just got tired of my logs filling up with people trying to break in. I still run the servers but just moved them all to different ports to cut down the noise.
Also, they have pretty crappy traffic management so even though I pay for 25/25Mbps connection, I can pretty much count on only getting that when speed checking on their servers. Any real traffic can never approach that, even in aggregate.
No problems there either. I frequently actually get higher rates than I'm actually paying for and have been seeing that on all the various plans I've had over the years. I'll see sustained rates (30+ seconds) about 2-5Mb higher than my "limit", but I'll see spikes (2-5s) 10-15Mb over.
I have a lot of complaints about Verizon and FiOS, but the Internet portion of the service has always been top notch for me and is the only reason they keep getting my money (no one else that serves my neighborhood can compete with the speeds/price Verizon offers).