Load balancing - Hardware or Software

Most of my load balancing experience is with F5 BigIP LTM.  This has served us well for a good number of years.  Recently I am left with a feeling that we should revisit this.  The hardware is getting older and is now showing signs of impending whole hog failure.  To top it off, the budget line items for replacements keep getting scratched off.

What are the options?
 Either more F5 equipment or maybe Citrix NetScaler or other hardware?
 On the other hand, we could go out on a limb with software load balancing.

What are the benefits of HW load balancing?

1. Major features (of importance to us)
1. SSL termination
2. Load balancing
3. Rewriting
4. Caching
2. Efficiency
3. Ease of use
1. TCL used for language
2. Single point of SSL certificate management
4. Support
1. Nice to have someone you can call 

What are the downsides of HW load balancing?

1. Cost
2. (near) single point of failure (unless item 1 is not an issue for you)
3. Limited features

What are potential benefits of SW load balancing?

1. Potentially lower cost
2. Potentially less of a "single point of failure"
3. Handle high loads (notes below)
4. More features available
5. Flexibility 

There are downsides to SW load balancing.

1. More challenging integration (potentially multiple products used to implement feature sets)
2. Requires more in house expertise
3. Others - work in progress

Software Options

1. nginx
1. http://nginx.org/
2. lighttpd
1. http://www.lighttpd.net/
3. Apache Server
1. http://httpd.apache.org/docs/2.2/mod/mod_proxy_balancer.html
4. Apache Traffic Server
1. http://trafficserver.apache.org/
5. Squid
1. http://www.squid-cache.org/

Need to include some supporting information sites.  Would be good to do some proof of concepts implementations and some performance benchmarking.