I also tried very hard to have Evernote at the centre of my GTD-like workflow but as email is my most dominating source of tasks and reference material, having my email client at the core has been the only thing that has worked superbly. I must have tried 10 or more other systems, including RTM, gTasks, Toodledo, UltimateToDo and Springpad.
I didn't want to have to send from my email client to Evernote, adding subject line modifiers or tagging in Evernote when I can simply tag in Gmail (especially made easy by the free ActiveInbox plugin). Sure I could automatically transfer to Evernote with filters or services like ifttt, but it's just another thing to configure and emails requiring response meant back to the email client.
I decided I didn't want to be locked into Evernote's proprietary method of storing my reference material, opting instead for DropBox and its standard file-based organisation.
Gmail I have a calendar one click away for my hard appointments. No setting up required and automatic syncing to Android. The ActiveInbox plugin for Gmail allows the quick creation of emails (i.e. tasks) to oneself with the appropriate action/context/project tags. I email scheduled and recurring reminders to myself via followupthen.com so I completely have them off my radar until their time.
Evernote's three level hierarchy for storing reference material bothered me at first, preferring unlimited 'foldering', but I think I'm becoming a believer in its multi-level tagging over multi-level foldering anyway.
I dislike Evernote's crudeness. I did screen clips and css styling was lost, despite specifying to keep it. I did tables and a simple two column table would span the entire note width with no obvious way to change it. I pasted in images and couldn't reposition them by dragging. I'm sure there are ways around all this but I'm not prepared to waste time finding it if it's not intuitive.
I usually would have dumped such a program straight away, but I keep on coming back to re-evaluate it because I haven't yet got an efficient system for storing notes and web snippets and I'm trying to see what so many people see in Evernote.