I use SX3 primarily but I purchased a Reaper liscense because I want to encourage it continued devlopment (not that Justin needs the $$
)
The Reaper version 2 upgrade made some significant leaps. The addition of a fully functioning mixer is not groudbreaking as an idea but it was a much needed addition.
The default skin is really nice. I was a big "Reaper is ugly" advocate but the new look and advanced skinning capabilities shattered that shortcoming. If you don't like the default and you can't figure how to get a look that is usable than that is more of a user issue as the possiblities are as expansive as your imagination will allow.
Reapers routing is better than Cubase and pretty much anything else on the market - but the routing page GUI window is a design disaster and needs to be fixed - this is not a major gripe and easily fixable IMO.
Reaper is really the only DAW to properly utilize 8 core computers at lower latencies
I am primarily an audio guy so I can't speak to MIDI. Here are the hold out points for me on Reaper;
1) Does not properly integrate with UAD cards (I have 4 in a Magma Chassis) in a multicore environment - I love their plugs and this is a big issue for me. Reaper claims that it is a UAD issue - I don't really care as it works in Cubase
2) Reaper automation is clutzy, confusing and a PITA to use - Cubase with Multiple lanes for automation easily trumps it.
3) Hardware integration is possible in Reaper but it is not as slick as Cubase. Pro Tools HD wins in this category
4) I am not a fan of how Reaper manages comp takes. Cubase really shines here. It is easy and flexible to use. Reaper still needs some tweaks here
5) Group Channels are poorly executed in both Reaper and Cubase - PT is king again in this area but a huge margin
CONCLUSION
As some have mentioned Reaper's service is really outstanding. It takes a lot of guts to be so open with your customer base and this is where I have the most admiration for what Reaper is offering. Bugs are fixed fast, updates with usable functions are very regular. I beleive Reaper still has some work to do but based on how slow Cubase and Sonar are, it won't be long (1 to 2 years) before Reaper surpasses those two programs for audio. I don't think PT is any danger of losing their perch but it is going to be an interesting couple of years, cheers!