VPN capabilities are limited to pass through mode for one PPTP, IPsec, and L2TP client each. Port forwarding to one of each server type is also supported, provided you establish the proper Port Forwarding rules.
Logging and Other Features
The WRT55AG's logging features are the usual Inbound and Outbound traffic logs that you've come to expect with Linksys routers. But Linksys has some work to do since my multiple port scans failed to produce a single Inbound log entry, the Outbound log showed only IP addresses and port usage vs. URLs for Internet traffic, and you can't save logs to a file or clear them. Linksys has acknowledged the Inbound Logging problem and said it'll be fixed, but the other deficiencies remain "features" for now.
It also appears that the "detailed" logging mechanism is based on syslog, not SNMP traps. So don't believe the Help file info that tells you to download the Linksys Logviewer application, since it uses the older SNMP trap mechanism.
Other features worth mentioning are the ability to disable the Internet Sharing function and use the WRT55AG as a non-NAT router. When in this mode you can enable Dynamic Routing, but can't control any aspects of its operation - a step back from the level of control provided in the WRT54G. However, in either Gateway (NAT) or Mode, you can define up to 20 Static Routes.
The 55AG also includes clients for DynDNS.org or TZO.com's dynamic DNS services. I may be biased, since TZO both hosts SmallNetBuilder and provides our DNS, but if you're going to use dynamic DNS, you really should use a reliable service, which is one of TZO's strengths.
That about wraps up the features. Let's move on to Performance.